heating for greenhouse and fish

so i have another post under the fish page but the number of people that actually visit there seam to be pretty low.
I have a greenhouse with 2 fish tank - ponds in there. 1 is 800 gallon with trout, and the other is about 1000 for tilapia.
the Trout are fin with this cooler weather their tank is staying in the 60s without ant additional heating.
the Tilapia water temps had been getting low so i bought a cheap OnDemand portable water heater.
This was bought from Ebay for about $130. quite a nice little system for the cost.
the water heater is plumbed into a small propane tank and powered by 2 batteries.
I have a pond pump with a connecting hose feeding into the heater and an output hose that feeds into another hose weighted down with an old plant pot so it sits on the bottom of the tank / pond.
the outside temps here in Ohio have been getting into the high teens low 20's for the last few weeks.
I also have a home built solar heater that i use when the  sun comes out. (not too often at the moment)
well i,ve been managing to keep the Tilapia water between 70 -80 degrees, and the greenhouse temp has not dropped below 50 degrees.
I do also have another heater that is not installed yet just incase i need the additional help. this is a small heater that is designed to be used for campers, boats and semi trucks.
Its a diesel fueled Webasto type heater, I have one already installed in the wife's greenhouse and it works really well.

but I would like to know what other people are doing and what temps your maintaining  

Phil, did your question get answered on this thread?

https://permies.com/t/170923/Heating-fish

Hi Anne. no it didn't. apparently it a subject people have very little to talk about.

What is the name of what you are doing?  Is it aquaponics?  

You have a really nice setup.

I have read several threads here on the forum about what I believe is aquaponics.

The forum has so many really nice threads on things that I find so interesting.

Thank you for the reply Anne.
Yes it is an Aquaponics system. It has 2 tanks. an 800 for Trout  and a 1,000 for the Tilapia.
the Tilapia tank feeds into the pipe system and the Trout tank has floating plant trays.
the system is in its 1st year but i'm happy with it so far. though as with any project there have been issues.
The main issue at the moment due to the weather is Keeping the Tilapia warm enough.
I have an on demand propane water heater that I'm heating their tank with, the issue has been making sure the water supply is clean enough to run through the heater.
though i think i have that figured out at the moment. The water supply is from a sump pump in the tank but it would pick up any sediment and particles and clog the heater.
to get over this I wrapped the pump  with insect screen mesh and then in a fine mesh material. I do have an inline pond filter on order but it wont be here for a few days.
this filter also has a backwash for easy maintenance.

oh and have a great new year.

Phil

Sorry I don't have an answer to your question, but I do have a question, how much fuel are you using to heat with?

Thanks Tom

Happy new year Tom
the on demand water heater is using 1 20lb propane tank . (the BBQ size)
during the November and early December when we were constantly below freezing, it was using 1 tank per week.
with the weather being slightly warmer at the moment the tanks are lasting a few days longer.
the water temp is between 75 - 80 deg.
I also have a home built hot water solar panel that i run during sunny days. cant remember last time we had one of those though.
I get the water to about 80 deg before i switch off the  water heater for the night. usually the water temp has dropped to between 70 - 75 in the morning depending on outside temps.
It takes about 2 hours to bring the tank back up to 80 ish and then i'll switch it on in the evening for an hour or two to bring the heat back up to 80 if it has dropped too much during the day.

Regards Phil