Backyard Aquaponics
A place to discuss aquaponics

Hi, I’m from the US and I went to school at UGA where I helped UGAquaponics with their teaching demonstration. Now I’m a volunteer in the Philippines in the central Visayas, and as a secondary project I’m helping a local city agriculture office with their demonstration system which was set up by a previous volunteer.
The system is a 4.5 m^3 concrete tank (<4,500 L) with 3 x 55 gallon barrels cut in half for 6 grow beds (450 L). It’s a simple flood and drain system with gravel media in the beds. We run the 1/4 horse power pump 15 minutes every hour on a timer.

We alternate between pechay (pak choi) and lettuce. There’s currently 100 tilapia in there. It should probably be 3-5 tilapia per square meter when we get the summer heat because we don’t have any aeration besides the water draining from the grow beds for 15 minutes every hour. No solids filter, but they have worms in the beds.
PH has been the biggest problem. It’s regularly at 8.2 in the morning and 8.4 in the afternoon. The fish don’t seem to mind, but the plants have been growing slowly. It looks like the gravel they used is raising the pH. This was a problem from the beginning, and when I got here they were using muriatic acid to correct the pH. But that’s just a temporary solution, and they have a limited budget to get more. The last volunteer was experimenting with charcoal and plastic bottle caps in two of the grow beds, but I’m sure we have to remove all the gravel before we see any difference. I think we’re going to try coconut husks and wood chips in two more of the barrels. The challenge is to work with cheap and locally available options (we’re kind of out in the bundoks, literally). It makes me miss when I could just drive to a hydroponics supplier in the States and get whatever I needed, but I guess this is the thrill of the challenge. I'd appreciate any comments or suggestions. This is kind of a learning process for me and my local counterparts.

Welcome to the forum

I like the simplicity of this setup. You might want to check the water source pH as well (and after it sits for a day) but it does sound like the rocks are the cause of the pH problems. If you have scoria locally that might be an option but test whatever you find with vinegar to see if it has carbonates and gives off bubbles. Wood chips and Coco Coir could be made to work but since they are organic, they will eventually break down and need to be replaced and that would be a recurring cost vs a one time cost for the scoria.

Hope this helps.

PS - If there is an easy and ample source of water you could add on some wicking beds to the system pretty easily. The water from the wicking beds wouldn't return to the fish tank so they could be below the tank level and just filled manually or by top up valve. You could also just irrigate the ground nearby if they want additional growing space. The main thing is not to pump the fish tank dry.

Hmm, concrete is very alkaline. Definitely test the top up water and the rocks, but it could be that leaching from the concrete tank is adding to the problem. Too bad fish safe epoxy or a liner are #1 expensive and #2 not available nearby. I hope you can figure it out.

You can support a lot more GBs with a pond that size. If the ammonia conversion is increased by adding GBs and feeding more, that might help drop the pH too. Not sure, maybe someone else has some experience here.

Excellent point. Try testing the existing rocks, maybe they aren't the problem .

Thanks for the advice!



I've been asking around about lava rock and scoria, but it sounds like people aren't familiar about it and where to get it around here. Being part of the department of agriculture with a few demonstration operations, it's easy to get things like coconut coir, wood, vermicast, and rice husks free or for cheap. We're going to try it for the next cycle of plants, see how it goes!



I like that idea. We have an extra 55-gallon barrel half that's just sitting around. We could put coconut fiber or rice husks and set up a wick.
I guess I didn't mention the water supply, but we filled the tank with a water tanker from the city. Otherwise, we'd have to use city water from the tap or pump water from a well 30 yards away and bring it over in buckets. Whenever the tank has needed a refill the staff has relied on requesting a water tanker. But I imagine we could support one or two wick beds and replace the water loss with the onsite water sources (I'd test the water quality first of course).