Aquaponic Gardening

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Hi to everyone, this is my first post

I live in central Texas and I'm building an aquaponics system. I started by building a concrete block tank and then built a greenhouse over the tank with lots of space for grow beds. When I originally built the tank I didn't realize that I would need to seal it from the concrete. I have now learned that the concrete block has a very high pH and will hurt the fish and plants.

I have looked a little at SanitTed PermaFlex and Epoxy Paints.
If anyone have tried these product or if you have used another product that has worked well, please let me know.
I include a picture of the tank and greenhouse. Thanks!

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Great to here it, Josiah. You can add a bit of wood ash to raise it if you have any on hand, or limestone, or seashells, or coral sand, or concrete. I'd get it in the 6-8 range, and get some ammonia in there and start cycling up. No need to adjust pH while cycling, just let it drift until ammonia and nitrite have both spiked and fallen, and you're ready for fish. Plants can go in anytime, even with a pH of 5. Good luck

Thanks so much!

Hi Josiah, how it went the ph, you got in the range now?

Hi John,

I'm just now seeing your message... Yes the pH seem to be right now, about 6.5. I hopefully will get fish soon!

Thanks for checking on me,


If you have any problems later with the PH or it starts leaking you can try using a epdm pond liner with a geo textile underlayment. 

I have similar problems like Josiah. I have just finished this watertank, diameter 5,2 m en 3.20 m deep.

It will be used to keep tilapia and harvesting rainwater for irrigation. My problem is the separation of the cement walls from the rainwater to not affect the ph of the rainwater.

If I were to follow the advice of Ian Cameron to paint with epoxy, what problems could arise, besides the fact that cement will not adhere to the epoxy paint?

Ian what primer should I use for the epoxy paint?

John S. If you're just using your tank for tilapia and irrigation, don't worry about pH. Get it a good scrub with saltwater when you're done with cement, and let it fill. Tilapia and algae enjoy high pH, and the soil will buffer it anyway when used for irrigation.

I agree with Jon Parr.  Too much is being made of high pH.  I've built concrete tanks and placed Koi in after a couple rinsings without any problem.  Eventually the concrete will not affect the pH at all.

Jon & Bob, the irrigation water I need should be 6,5  for the tropical fruit trees I grow. I build this tank as I allready have two wells with brackish (3700 micro siemens) and high ph water which affects the trees and the clay soil (iron chlorosis).

That's why I am asking if the epoxy paint will isolate the high ph cement. The tank is to big (65 cu.m) to be rinsed.


@John - Swimming Pool Paint

Here is an update for anyone interested...

I put together a small group of pictures of my project and decided to share them here.

I don't have tilapia yet but I did get some goldfish that seem to be doing good!

I'm working on finishing the grow beds as you can see and then I'll be ready for plants and fish!


Bob Campbell, I painted with swimming pool epoxy paint. The ph is 6.8 the salt level is 38.

So everything came out perfect for my fruit trees and fish. With the last rain the tank is full till it overflowed.

That's 70 cu meters= 2475 cu.ft. of clean rainwater. My only problem right now is some birds eating my fish. Thanks to all for the help.



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