# Help sizing DIY solar water heating for Aquaponics?



## Mallow (Aug 4, 2006)

First off let me describe what I have currently. I have an aquaponics system that has about 2000 gallons of water in total and looks like this:










In the Fall through Spring I raise 100 trout in the concrete tank. While growing lettuce in the grow beds. I use the water from a ground spring that flows into the system to help keep the water quality in check during this time frame. 


With all of that said I would like to grow catfish in the summer and would like to use solar heating to bring up the temperature range to 75-85 degree water for optimal growth. My idea so far:


1) Put another insulated IBC between the growbeds and the fish tank with a PEX heat exchanger inside and run a closed loop heating system separate from the fish water (algae and slime would clog things up fairly quickly in an open system). 

2) Use a differential controller to kick on and off the circulation pump when needed with temp probes inside the collector and IBC tote.

3) Optional use another controller to kick on a pump from the fresh spring to replace water and cool down the water once it reaches the 85 degree mark if the spring has water available at the time.


How would you go about figuring out how many SQ FT of collector would be needed for such a project or what more information is needed? I live in North Central WV and the ground water coming out of the spring is about 50 degrees. Any help would be appreciated.

Thanks
-Mallow


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## Mallow (Aug 4, 2006)

I decided to make the solar heater 8'x12' and to use a plastic drum for now for the best exchanger. I'll posy some pics once I get things moving along. Catfish being delivered by the end of the month.


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## SolarGary (Sep 8, 2005)

Hi,
A water heating solar collector will produce about 900 BTU per day per sqft of collector (more or less). If this is a summer only situation, you would probably be better off using the plastic mat style pool heating collectors (no glazing) as they are cheaper and more efficient in summer situations when you are heating water that you only want to get up to about 80F.

The hard part of determining how much collector you need is estimating the heat loss from the whole system of tanks. One fairly simple way to do this is to monitor the system temperature for a full day in which you don't add any new fresh water and you don't add any heat. How much the temperature drops over a day lets you easily calculate the heat loss for the whole system.

For example if the system has (say) (10*275 gal/tote) = 2750 gallons. And, it cools down by (say) 3F over a full day, then the daily heat loss is:
(2750 gal)(8.33lb/gal)(3F) (1 BTU/lb-F) = 687K BTU per day.
I just pulled these numbers out of the air -- you would have to do an estimate of your system water volume and then measure how much it cools over 24 hrs to get good numbers.

But, taking the example I used, you would lose about 700K BTU per day, and that would take 700000/900 = 770 sqft of collector. 
This seems like a lot, and I'd guess when you do the cool down measurement it won't end up needing this much collector.

If you are adding fresh water that is cold, you would have to account for heating that up as well -- we can go through that calc if its of interest?

There are some collector designs you might find useful on this page on pool heating: http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm
On the same page is a way to size collectors for heating hot tubs -- the method I used above is based on this method.

You could also consider insulating the tanks so that there is not as much heat loss. Keeping evaporation losses down will also reduce heat loss a lot -- just like a cover on a pool greatly reduces heat loss by stopping evaporation.

Gary





Gary


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## Mallow (Aug 4, 2006)

Gary thanks for the reply and I am digesting the math. Once I kill off the rest of the trout I'll take a stab and getting a few temperature readings to see what works out. It may just take to many sqft of panels to be worth it at the ment for me.

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Hi,

If it does turn out that you need a lot of collector area, there is an interesting collector design for a similar application on this page:
http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#GreenhouseHeat

Search down the page for "Rutgers"

Its a very inexpensive design, but requires more maintenance than other designs.

Gary


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## Mallow (Aug 4, 2006)

Gary,

Would you suggest a commercial type of pool heater over a DIY? It seems that some of the cheaper pool collectors (Fafco 4'x20') would probably come out cheaper and more efficient that trying to make my own. I would still need to make a racking system of sorts for it of course.

Thanks
Mallow


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## wy_white_wolf (Oct 14, 2004)

I'm wondering how you are going to keep a fairly constant temperature supplied to the fish. Giving them 80F to 90F water during the day and then down to 50F water at night will spell the death of catfish. You're going to have to come up with a good sized storage and tempering system to make it through the night (let alone any cloudy days). 

WWW


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## Mallow (Aug 4, 2006)

I'll need to wait to do the testing after killing the trout but I don't think it will cool off more than a few degrees overnight. I definitely won't be letting spring water in unless I have it above 80 degrees so it is just what it drops during the nights. It is an experiment for sure and I have killed a few trout before getting it right so probably I'll lose some catfish.

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> Gary,
> 
> Would you suggest a commercial type of pool heater over a DIY? It seems that some of the cheaper pool collectors (Fafco 4'x20') would probably come out cheaper and more efficient that trying to make my own. I would still need to make a racking system of sorts for it of course.
> 
> ...


Hi Mallow,
Yes -- I like the Fafco style pool heating collectors. I've never compared the price of the Fafco style ones with the DIY pipe coil ones, but they can't be much different. I'm a dyed in the wool DIYer, but this seems to be one case where it makes more sense to use the commercial product.

The exception might be that Rutgers style collector, which would be very cheap but probably also much higher maintenance.

Ebay usually has some pool heating collectors listed, and they can be pretty good deals.

WWW makes a good point. I think the cool down test will tell you a lot about how fast the system will react. As you say, you might be able to time your introductions of spring water to reduce the temperature swings.
Insulation might also help.

Please keep us posted.

Gary


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## SolarGary (Sep 8, 2005)

Hi Mallow,
This link is the SRCC test on one of the Fafco pool heating collectors:
https://secure.solar-rating.org/Certification/Ratings/RatingsReport.aspx?device=224&units=USUNITS

It gives output for pool heating (classes A and B). They show that when its sunny you should get between 1300 and 1900 BTU per day per sqft of collector -- so, quite a bit better than the 900 BTU per day per sqft I gave you above (which is more typical of glazed collectors in the winter). The collectors are quite efficient for this kind of application -- up around 80%.

As an example, 300 sf of this collector at 1500 BTU/sf-day would get you about 450,000 BTU per day -- like burning 6 gallons of propane in an 80% efficient heater.

They also give output numbers for part sunny conditions.

Gary


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## Mallow (Aug 4, 2006)

Gary, 

Do you see any reason these wouldn't work in a closed system? I think I'll go ahead and order some to have here for testing. I need to pick a pump also but have the stuff here for a heat exchanger already using pex. That's a lot of but per panel and I'll do testing while on the ground before designing a racking system.

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> Gary,
> 
> Do you see any reason these wouldn't work in a closed system? I think I'll go ahead and order some to have here for testing. I need to pick a pump also but have the stuff here for a heat exchanger already using pex. That's a lot of but per panel and I'll do testing while on the ground before designing a racking system.
> 
> ...


Hi,
They would work with a closed system using a heat exchanger to transfer heat to the fish/grow tanks. 

I'd look into using a coil or so of the black HDPE pipe that the hardware stores sell as your heat exchanger -- I'd get the stuff with the NSF (safe for drinking water) stamp. Its fairly inexpensive. Its limited to about 140F, but that should not be a problem for your setup.

You could also use a coil of PEX, but its more expensive, and does not really seem to be needed for this application.

The question is how much to use? You want enough so that there is not a large temperature drop from the collector loop to the tanks, as this would cause the collector to have to run hotter and reduce efficiency.

I'll see if I can get a better number, but as a gut feel, I'd say that a 300 ft coil of 1.25 inch diameter would not be too much.

I'd recommend keeping it in the bundled coil until you get it into the tank you want to transfer the heat to, and then cut the bands and spread the coils out with spacers. Some people try to recoil on some kind of form for better efficiency, but this is a major hassle to do.

These pool heating collectors normally have pretty high flow rates through them as they are typically driven by the pool pump. On conventional glazed collectors, the usual flow rate is from 0.03 to 0.08 gpm per sqft of collector. I would shoot for the 0.08 or even a bit more end of this for the pool heating collectors. The reason for shooting for a fairly high flow rate is that with the high flow rate, the water heats up only a little as it goes through the collector and this allows the collector to run cooler and lose less heat to the air which makes it more efficient.

I'd also consider running the system open loop with a filter on the collector inlet. Maybe this is not practical, but it would be more efficient and would save you some time and money.

Laying the collectors out on the ground should be fine. The sun is high in the summer, and even lying flat they should do fine. You will want to think about some way to drain them for the winter.


This would make a great project for BuildItSolar -- take pictures 

Gary


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## Mallow (Aug 4, 2006)

Gary,

I will be sure to take alot of pictures and document the project. I always do  

I was going to use only 100' of 3/4" PEX as the heat exchanger but that seems like it will be way to small. I found this at homedepot:

http://www.homedepot.com/p/Unbrande...e-Pipe-AJ101030/100124369#product_description

Would that work you think? Its up to 200 degrees but only 1" but it is cheap enough to fit the budget.

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Hi,
I think that the coil you show is rated at 200 psi pressure -- I don't think you need this, and the lower pressure ratings are cheaper.
I may be remembering wrong, but I think that the last 300 ft roll of 1 inch I got was was only $70 -- this was probably 5 years ago.
I got my coil at a local plumbing supply house.

This does bring up one thing that I had not thought about, and that is that if you run the system closed loop you will need a way to keep it from developing any internal pressure. The pool heating collectors are not designed to take internal pressure.
Not sure exactly how you do this, but one place to take a look would be Scott's site -- he worked out a simple way to regulate the pressure in his closed loop system -- he talks about it a little on this page: http://www.n3fjp.com/solar/construction101/construction101.htm
search down the page for "iced tea jar". I'm sure he would be happy to answer questions about it.

Did you conclude that there is no way to run the system open loop with a filter?

Gary


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## Mallow (Aug 4, 2006)

Gary,

With all the fish poop and plant roots/matter floating around and using a raft type system the filter would be a no go. I would have to switch it out probably daily. I was going to get an expansion tank to add to the system and I thought that it would take care of the pressure in a closed loop system? I will take a look at the link provided.

Thanks for the help so far.
-Mallow


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## Mallow (Aug 4, 2006)

Most of the poly pipe I am seeing is listed as 80 degrees max temp. I want to make sure I get the correct type. Most places around here seem to sell ADS poly pipe but can't seem to find any information on their website about the max temp. Any suggestions on what I should be looking at?

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> Gary,
> 
> With all the fish poop and plant roots/matter floating around and using a raft type system the filter would be a no go. I would have to switch it out probably daily. I was going to get an expansion tank to add to the system and I thought that it would take care of the pressure in a closed loop system? I will take a look at the link provided.
> 
> ...


Closed loop systems with expansion tanks are typically run at about 15(?) psi internal pressure and the expansion tank takes in or lets out water to keep it at that pressure. I think you need to run at a lower pressure than this with the pool heating collectors, and I'm not sure if an expansion tank can be set up to do this? The expansion tank might work OK at a lower pressure -- just not sure.

Gary


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## Mallow (Aug 4, 2006)

After looking at your link about the ice tea jar and knowing that the pool heaters can't take much psi it may be better to do a method like that instead of an expansion tank. I could either use a 5 gallon bucket or an extra 50 gallon plastic drum. To allow for the expansion and not build it pressure.


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## Mallow (Aug 4, 2006)

300' of pipe coiled into heat exchanger. A lot of zipties were harmed in the creation.


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## SolarGary (Sep 8, 2005)

Mallow said:


> 300' of pipe coiled into heat exchanger. A lot of zipties were harmed in the creation.


Nice!
I like the PVC T's as a way to space the coils.

When you plumb it in, it would be nice if you could work out a way to measure the temperature coming in and going out of the heat exchanger -- this would allow us to see how good a job its doing and whether the heat exchanger is causing much of any hit on collector performance.

Gary


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## Mallow (Aug 4, 2006)

When doing a quick search all I see are sharkbite temp gauges. I need to get a pump selected and then I can see about the incoming/outgoing temps for the heat exchanger. My house radiant floor system uses a grundfos pump and I have been happy with it. May try to find a similar one for this system. I cut down the IBC tote today and working on washing it out before cutting holes for uniseals. Ill post some more pictures when that portion is done and in place. The black pipe was a giant pain doing it by myself when it wasn't warm enough to make the pipe softer. I would recommend a sunny day and some help that's for sure.

-Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> When doing a quick search all I see are sharkbite temp gauges. I need to get a pump selected and then I can see about the incoming/outgoing temps for the heat exchanger. My house radiant floor system uses a grundfos pump and I have been happy with it. May try to find a similar one for this system. I cut down the IBC tote today and working on washing it out before cutting holes for uniseals. Ill post some more pictures when that portion is done and in place. The black pipe was a giant pain doing it by myself when it wasn't warm enough to make the pipe softer. I would recommend a sunny day and some help that's for sure.
> 
> -Mallow


For metal pipes, you can tape the temperature sensor tightly to the outside of the pipe with a bit of silicone or conductive grease to improve the thermal contact, and then insulate well over the whole area around the sensor. I'm not sure how that would work for poly pipe as its less conductive. Maybe use one of those metal barbed couplings for poly pipe as a place to mount the sensor?

I have used a setup with a T in the line, and then put a cap on the branch of the T with a small hole drilled in it for the sensor. The sensor is pushed through the hole far enough to be in the main flow, and then the cap is filled with silicone to seal it. This works fin in my drain back system where the pressure is pretty low. The sensors I have are metal cylinders about 1/4 inch in diameter and the same diameter as the wires coming into them, which makes it easier to use this technique.

Gary


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## Mallow (Aug 4, 2006)

I ordered the Grundfos pump, pump flanges and 2 4x20 Fafco Panels today. Hopefully they will be here before to long and I can get things in place. Stopping by Lowe's to buy the insulation and lumber to insulate the IBC tote. Going to be a busy week I can already tell.

-Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> I ordered the Grundfos pump, pump flanges and 2 4x20 Fafco Panels today. Hopefully they will be here before to long and I can get things in place. Stopping by Lowe's to buy the insulation and lumber to insulate the IBC tote. Going to be a busy week I can already tell.
> 
> -Mallow


Great! 
Please keep us posted.

Gary


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## Mallow (Aug 4, 2006)

Ran into a slight problem....a black bear raided my aquaponics last night:










He broke the growbed plumbing and 2 of the rafts. He also got several trout it seems from just looking in the tank. I guess an electric fence is in order before the catfish.

-Mallow


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## Jim-mi (May 15, 2002)

Or a 30-06 . . . . . . .
Got a neighbor who likes bear meat . .??

electric fence just might make it madder ......
Once it has found a tasty trout meal at your place. . . . .It will be back.....

good luck...........


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## Mallow (Aug 4, 2006)

Pulled the last of the trout out of the system. It appears the bear took more than I had imagined. I would have to guess over 40.










The largest I had left was about 15 inches at 26 ounces. Not to shabby.

-Mallow


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## Mallow (Aug 4, 2006)

Just an FYI. I have everything plumbed and will be turning off incoming spring water tomorrow morning to do some testing. I will do a few temps throughout the day to see how fast it is raising.


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## Mallow (Aug 4, 2006)

Still under contruction but early testing seems to say its going to work. I don't have everything finished up nor do I have the differential controller wired in yet but by just running the pump today it seems like it will work. The water started out at 56 degrees this morning when I turned off the incoming water. Currently it is 71 and still rising but I will just the final temp before turning off the circulation pump this evening when shade hits the panels.


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## Mallow (Aug 4, 2006)

56 to 74 today on a nice sunny day. I'll see what it is tomorrow morning for heat loss.


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## SolarGary (Sep 8, 2005)

Mallow said:


> 56 to 74 today on a nice sunny day. I'll see what it is tomorrow morning for heat loss.


Getting close -- will be interesting to see what the overnight loss is and how well it recovers tomorrow.

How close to the 80F do you need to keep the temperature? That is, how much can it vary over a day or two without causing the fish trouble?

Gary


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## Mallow (Aug 4, 2006)

Well based on research they grow well from 70 to 85 but I'm not sure how temperature changes effect them. I have only raised trout so far. We shall see that's for sure.


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## Mallow (Aug 4, 2006)

So last night we had rains and the open growbeds i'm sure caught some of it. The temperature was 72 this morning when I checked so it lost around 2 degrees which is pretty awesome.


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## Mallow (Aug 4, 2006)

Gary,

I started hooking up the Caleffi differential controller (iSolar 2). My thermometer wires are to short so I will need to extend them if possible. Can I just use any wire or does it has to be specific?

Thanks
Mallow


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## SolarGary (Sep 8, 2005)

Mallow said:


> Gary,
> 
> I started hooking up the Caleffi differential controller (iSolar 2). My thermometer wires are to short so I will need to extend them if possible. Can I just use any wire or does it has to be specific?
> 
> ...


Hi,
The Caleffit I have uses 10K thermistors for the sensors, and the wires can be extended a long ways with no problems. Since the sensor is just a resistor, there is no polarity to worry about.

If the Caleffi is intended for a conventional solar water heating system, you may have to do some experimenting with the settings for the turn on and turn off differential -- I think the turn off differential is going to have to be quite low for the swimming pool collectors. 

The collector sensor should be placed near the collector return so it sees the hottest part of the collector. The problem you may run into is that the collector will warm up quickly with no flow and this will cause the controller to turn the pump on, then when flow gets going, the collector will cool down due to the flowing water, and the pool collectors work with high flow rates, the collector may cool down to just a couple degrees over the tank temp -- this is fine and efficient, but the controller may think there is not enough temp gain to keep the pump on, and turn it off. This ends up causing short cycling. But, if you set the turn-off differential down low, it should be OK.

Gary


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## Mallow (Aug 4, 2006)

The lowest difference this controller seems to do is 6 degrees. Hopefully that is low enough that it doesn't keep cycling but we shall see. I have a 3 speed pump so I may need to slow down the pump to medium instead of high if it keeps forcing it to turn on and off as the water passes through. The catfish arrive this evening so here goes nothing I guess.

-Mallow


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## Mallow (Aug 4, 2006)

Thanks Gary, extending the cable worked perfectly. I will watch it a few days to make sure it isn't cycling the pump to much. I still have to button a few things up and fix some plumbing bear damage today before the catfish arrive. I hope the rains hold off till then.

-Mallow


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## K.B. (Sep 7, 2012)

Just wanted to say that I am enjoying this thread and I hope your system works well for your catfish!


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## Mallow (Aug 4, 2006)

A slight change of plans the fish place only had to small of ones available on the truck for delivery. I found a different hatchery with larger ones and will be getting them next week instead. If I started with such small catfish they wouldn't be large enough before trout had to go back into the system.

-Mallow


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## Mallow (Aug 4, 2006)

The fish truck called me and said my fish will be here tomorrow. I will have to meet him about 5 miles from my house but should go fairly smoothly I think. I finished up the insulated heat exchange tank along with the pump and controller housing on the side of it. The black barrel is the open air expansion tank as suggested by Gary. The water this morning was 78 degrees and its been somewhat sunny all day. Hopefully I can get it a little warmer than that but its been raining off and on for a few days.


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## Mallow (Aug 4, 2006)

The catfish are now in the system. The sizes are pretty diverse ranging from 9 inches to like 14 inches. I did a small video of the system. Don't mind the mess and failed experiments laying around.

-Mallow

Solar heated aquaponics: http://youtu.be/AM6qTIcx4ZY


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## SolarGary (Sep 8, 2005)

Mallow said:


> The catfish are now in the system. The sizes are pretty diverse ranging from 9 inches to like 14 inches. I did a small video of the system. Don't mind the mess and failed experiments laying around.
> 
> -Mallow
> 
> Solar heated aquaponics: http://youtu.be/AM6qTIcx4ZY




Nice!

Does it look like the 160 sf of collector is going to do it?

It looks like the temperature drop of the system is a fair bit at night -- maybe due to adding fresh cold water? Or, just a lot of heat loss?

Gary


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## Mallow (Aug 4, 2006)

It is just loss of heat because the fresh water coming in is mostly turned off. yesterday when I checked it was at 77 degrees and anything over 70 will be fine. The catfish still aren't eating yet but it always seems to take a few days. I did have one escape through the hatch overnight the first night. Who knew catfish jump more than trout. I have since latched it down better.

-Mallow


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## Mallow (Aug 4, 2006)

I just wanted to stop by and update the thread. So far the heaters seem to work well but doesn't completely get it to the temp I was looking for. It hovers around 80 degrees and will stay there but it has been cloudy and rainy so I will give it some more time. I have been purging dirty water and adding clean water when it gets close to 80 and sunny now and it has been working well. The catfish are still scared compared to the trout and I rarely get a look at them so I have no idea how they are doing.

-Mallow


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## SolarGary (Sep 8, 2005)

Thanks for the update -- please keep us posted.

Gary


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## Mallow (Aug 4, 2006)

Catastrophic Failure:

After crazy winds and driving rain some got into the load panel supplying the fish stuff. GFCI tripped and backups didn't take over either. 50 dead catfish for this season. The good news is the heater works but I need to protect the electrical more I guess.

-Mallow


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