Aquaponic Gardening

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Comment by Bob Campbell on September 5, 2012 at 8:41am

@Jon Parr - I see you point.  I thought the issue was about concrete buffering the water and keeping it in an alkaline state. 

Comment by Jon Parr on September 5, 2012 at 3:45am
I wouldn't say 8.2 is "not a problem" in Aquaponics. Concrete tanks are great for fish and ponds. But it most certainly buffers pH up, and I have yet to see any reliable testimony to the contrary. Veteran pond builders argue tooth and nail that pH is not a problem in concrete, and I agree, for typical pond purposes. Nitrifying bacteria counteract the pH buffering, and the ponds balance nicely in the 8's, good for fish, algae, and water plants. Old ponds have more base concentration due to evaporation, and equally more acids to counteract due to anaerobic bacteria producing acids. But to say concrete is not going to affect the pH in a proper AP environment, is IMO untrue. Veggies want a pH of 6-6.5, and that will cause concrete to erode and release alkali, raising pH and requiring constant addition of acid. True, pH must be monitored anyway, and for me acid is a regular duty to treat my top up water, but much more so for concrete tanks. Thoroseal is more stable, but only down to 7.2, below that erosion and buffering will occur. If you don't believe me, try keeping your pond pH around 6.5, and then tell me it's not an issue. If you can keep it at 6.5 for a week without acid, I'll be impressed, and build myself some damned fine concrete fish tanks (because I hate plastics and their marriage to AP)
Comment by Bob Campbell on September 3, 2012 at 2:49pm

@Jon Parr -The other day I wrote "I used a lot of concrete when I built my pond.  It does not have any problem with pH"   The pond is not something I test very often and the pH is of little concern to me since everything grows so well without my attention.  So I thought I had better make sure I was not saying something that is not true.  

So yesterday I tested the pond's pH.  It read 8.2 pH which is about what our water tests at too.  I then put 600ml of 14% HCl acid in.  I measured it about 24 hours later and it had dropped to 7.8 pH.  I then put another 300ml HCl in and measured it at 7.4 pH 6 hours later.  Here are the results.  The colors in these tubes have changed slightly over the past 32 hours but as you can see the water is not severely buffered by the concrete.

The bio filter is 7'x3'x3' inside dimensions and built of concrete block, which is sealed by ThoroSeal.

The water falls and first 18" around the edge are concrete and rock,

The pond contains about 1100 gallons of water and is about 9 years old.

Comment by Claudio B. Maxwell-Merrill on August 30, 2012 at 11:06am


Bob / Jon Parr, thank you for the feedback. The system is located within Sweetwater Aquaponics. So far this experiment is working great. The water chemistry is balanced out and is holding life. It even serves as a bee watering hole LOL. This photo was taken early July. I will post updated photos later. Have fun growing!!

Comment by Bob Campbell on August 30, 2012 at 12:52am

@Jon Parr - I used a lot of concrete when I built my pond.  It does not have any problem with pH

Comment by Jon Parr on August 29, 2012 at 10:05pm

Claudio, I followed the link to Friendly's. Be wary of their advice. They have said many things contrary to common knowledge (worms causing e coli, and in the same breath as saying gator-ponics is safe, and more). I am indebted to their contributions to the industry, but not everything they say checks out, so be wary.

Comment by Jon Parr on August 29, 2012 at 9:48pm

Bob, it is my understanding that concrete is always going to buffer pH up. As long as cement is present, then so is Calcium, similar to limestone or seashells in your media. True, is will lessen, but never quit buffering up. Perhaps this is desirable if using very soft water or rainwater, but not hard water like I have.

Comment by Bob Campbell on August 28, 2012 at 6:00pm

@Kntryhart - This is a good information from Claudio B. Maxwell-Merrill

I would also suggest letting the system settle in before adding fish.  Balancing pH is tricky and until it settles in you will continue to get some wild pH swings. This goes for media too.  Be sure to add your media and let it settle in too.  This can all be done while building bacteria (cycling).

Comment by Claudio B. Maxwell-Merrill on August 28, 2012 at 3:34pm

 If the intended use is for aquaponics;  Yes, It could be made PH neutral see link below as an example

This is from the aquaponics news letter


Comment by Bob Campbell on August 27, 2012 at 9:23pm

@Kntryhart - Concrete only affects the pH for a short time. After the buffers are gone pH will be fine

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