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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@Chris - Your method does seems sound. I can imagine how the paraffin would soak well into the porous surface and create a smooth finish. 

I'm wondering if you would describe your method, and describe how you applied the paraffin while in a temporary liquid state. 

If done incorrectly this could result in disaster.

I have a vision of you inside a tank with a small electric stove and a double boiler cooking blocks of paraffin. 

Josiah, if the call were mine, and after reading the experiences here, I would do this: one coat of Thoroseal, one coat of pool plaster, then melt in paraffin as per Chris's instruction. The Thoroseal should properly waterproof it, the plaster will brighten it up, and can be burnished smooth and shiny like glass, and the wax will keep pH from being affected. 
If Thoroseal is not suitable for pH below 7.2, then acidic conditions are likely to erode it, and it will be an eternal battle to keep pH below 7.  Keep in mind that 7.2 is ok, just not great, and enough effort is being expended here that great should be the goal. 
Thanks Vlad, for linking that wealth of information.  It's been open on my desktop for two weeks, and I hadn't got that far yet. Good stuff.

I went to a yardsale and purchased an old large pot and a hot plate for $5. I break up the paraffin into smaller chunks and melt in the pot. Once melted and at a very liquid state I had a little less than 1/2 hour of working time before I it needed reheating. I paint on the wax with a large paint brush. The wax does not soak in at this point it just sticks to the sides.  There will be many voids that get no wax at all but its ok because once the wax is heated it all evens out as it is absorbed into the concrete. If there is a spot of no coverage after heating just apply more wax ahd reheat. The following coats even out and stays on the surface instead of being absorbed once heated. Using this method you can build up very thick wax coats if you wanted to.

Prior to coating my tanks I had a high pH issue due to leaching of new concrete. It wanted to stay in the high 8s.  After spending a small fortune in vinegar at Costco and then crashing the system with citric acid, I decided to fix the source of leaching. When I decided to wax my tanks they were in service so I had to move fish, bypass, and drain them individually to work on. I had to drain,dry, and coat in as short of time as I could. Once each tank was drained I dried the concrete with a weed burner. It took 10 gallons of propane to dry both tanks. Once dry I applied the first coat then heated in the wax. I applied a second coat and heated again. That was just about 2 years ago and the water still beads off the sides. I was able to coat both tanks and get them back in service in one LONG day. After coating I never had a high pH issue again.

Jon that's a good idea about the white plaster.  Thoroseal comes in grey and white so you might want to start out with white, on the other hand applying white plaster over grey would show you where the light spots are.

A tank this deep is going to be difficult to see into and white is going to help a lot.

Jon Parr said:

 The Thoroseal should properly waterproof it, the plaster will brighten it up, and can be burnished smooth and shiny like glass, and the wax will keep pH from being affected. 

This is wonderful info!

I like your ideas, I'm not familiar with the pool plaster, would I be able to get a little more info on this?

Thanks so much!

Hey Chris,

Thanks again for writing all that out, can you give me an idea how much wax you used. Also if you know of a good source to purchase it I would appreciate a name or link.

I got my paraffin at a local crafts store. It is the main ingredient for making candles so find a candle store. It is a by product of the petroleum industry and plentiful in some areas where there is a lot of production. I used 30 pounds to coat a 1000 and a 600 gallon tank.


Hi to all!

Sorry I haven't written sooner, but wanted to give everyone.

I applied three coast of Thoroseal and for looks on the last coat I add a red tent to the Thoroseal. Then I applied two coats of paraffin wax.

Everything seemed to work well. I added gutters to the greenhouse have the option of having the water coming right into the tank from the roof. Starting a month ago anytime it rain the water would go into the tank.

After a couple of weeks I tested the PH in the tank and sadly found it very high 8.2. The rain water had been about 6.8...

Not sure what to do, I decided to do a test I added several gallons of vinegar to the 2,200 gal of water in the tank. The vinegar lowered the PH to 6.1 :-) but a few days later it is climbing back up :-( now 7.4.

Any ideas on what I should do?

I don't have fish yet, just trying to get the PH right.

Thanks to all,


Looks good, Josiah. I wouldn't say all is lost just yet. The acid could be fighting the buffers in the water, regardless of container. First off, never use vinegar, it is antibacterial. Hydrochloric acid (muriatic acid)is cheaper and more effective, and won't harm fish, plants or bacteria if added slowly (no more than .2 change per day). Keep adding small doses and hopefully the calciumin the water will get used up and pH will stay down. Nitrification will continue to acidify, offsetting hard top-up water, and any leaks in the wax film that may exist. Is your system already cycled, plants growing, etc? I'm assuming not, especially if vinegar was used. I'd add acid until water stabilizes pH, and then don't worry or alter pH until system is well cycled, with fish and plants present, for a couple months. Chances are it will naturally fall into an acceptable range.

Thanks so much!

You are right in guessing that it is not cycling, I do have an air pump in the tank and a water pump hocked up so I can move the water around, but it is not going through the grow beds.

I'll try the acid like you recommend and let you know how it goes.

Chris, if you are still about, I would love to know what your pH is...

Thanks again,


Hi Jon,

You have given me much hope! I got the Hydrochloric acid like you recommended and added it the same day you wrote. Unfortunately I over did it when I was adding it :-(. I dropped the pH to about 5. (good thing I don't have fish) The good news is that it seems to be staying there.

At this point is there any thing you would recommend? There are small chances of rain the next 7 days so I'm hoping we'll get some. I have the water come right into the tank so that would help it I think.

Sorry to cause trouble, but I'm very thankful for your help and advice!


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