Aquaponic Gardening

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I have had to focus on the pH for a couple of weeks. It was gradually dropping into the low 6's and in the process I found the nitrates on the rise. I did a 25% water change about a week ago. Yesterday I tested the water and found the pH at 6.4, but the ammonia was at 1 ppm and the nitrate had risen to 80+ ppm. So I did another 25% water change to bring those numbers down.

My catfish don't usually turn down a meal, but yesterday morning they had no appetite. I'm thinking those high numbers were effecting my fish. I have not fed them since yesterday and I did remove what they had not eaten. So, Tell me what to do.

For the pH, yesterday I found some sea shells and I put a few in the sump tank next to the pump. Hopefully that will gradually raise the pH.

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  I have the option to use a small sized pea gravel or Dept. of Transportation road base gravel so I use a bit of both in my media-based grow beds.  My well water is very acidic, yeah like 4.3.  NO LIE!!  We have mostly pine trees here so there you go.

  With the DOT road base (which sometimes you can acquire for free, just go to the road maintinance building and ask for a bucket full, don't need much) the water flowing out of it is 7.2 immediatly because of the limestone pieces.  If you can get a hold of some limestone chunks, I would use that as seashells take a bit of time to do the job as they have to break down a bit.

White Bear

I went back and reviewed "the book." According to Sylvia, the high ammonia could be my over feeding the fish. She also says the high nitrate "is good news!" Oh, and build more beds. Well, we had planned to build an 80 sq' 600 gallon DWC, but not so soon.

Those numbers will affect the fish's appetite!  You're doing the right thing to reduce the ammonia. Feed less, remove excess food, and if you expect to stay overstocked for a while, have a fish dinner or two or three. :)

Are your nitrites high, or just ammonia and nitrates? Yes, nitrates are good because that's what feeds your plants, but they can be dangerous when too high.

Here's another idea you might consider in addition to fish dinners and more growbeds: Set up a duckweed tray. Duckweed consumes a lot of nitrates & can help control the levels noticeably. You can add a small pump that runs into a tray about 2-4" deep. Depending on your setup, it can drain back into the fish tank or sump through a screened drain (you can get them from the hydroponics store.) You don't want it getting to the growbeds, though, so be cautious.

Catfish are not very good duckweed eaters, so you would probably want to add some goldfish to the return tank to eat any duckweed that makes its way down the drain. That would keep it from getting anywhere else.

We have over 500 gallons of water and 40+ large tilapia, and we added a tray of duckweed to help control nitrates while we were cycling our new system. We saw a noticeable drop using a 3'x4' hydroponics tray. We use the duckweed for the tilapia and for chickens, so we can control the amount of duckweed, too.

Yep, if you are seeing ammonia and your pH is in a measurable range, then you don't have enough filtration for the amount you are feeding the fish.  You might need to circulate the water a bit more if you are on a limited pumping schedule you might need to pump more.

But as noted, you need more filtration and plants to help keep up and you need to feed the fish less.  Perhaps eat some fish and the idea for a duckweed tray is a good one.  Even a mortar tub will do.  Duckweed not only eats nitrates but it actually loves ammonia more, it can help remove ammonia directly.

If you have a big gravel bed and not enough plants going because it is too hot, I'll recommend some lufa.  (buy a sponge from me and mention you want the seeds too and I'll be sure you get a sponge with extra seeds so you can plant them.)  Beware, lufa can grow huge and totally block a bed with roots, consume a 30 foot oak tree and rip down your shade structure, but it will suck down nutrients like nobodies business.  One lufa plant in my 300 gallon system last summer brought the normally high nitrate level down below 5 ppm even with a heavy load of bluegill being fed 3 times a day.

Watch how many sea shells you put in your sump.  I've heard that they don't raise pH quickly but that they certainly raise pH a few days after adding them.  Being new to aquaponics I cannot offer you anymore advice.  What is your normal nitrate ppm and ammonia ppm prior to your fish not being "happy"?

TCLynx - what do you mean "and your pH is in a measurable range"?  I know ideal pH in aquaponics is 6.8.  Thanks for sharing any knowledge you can pass along! 

ps duckweek?, think I need to look at always having some of this on hand.

If pH suddenly falls way way low fast, it can cause the bacteria to stall out and the ammonia will spike.  This can sometimes be hard to detect if people don't realize that the pH test kit that only measures down to 6, "ONLY Measures Down to 6"  As in some people figure that is fine but the truth is if it reads 6 it could be anywhere below 6 and could actually be too low and the bacteria could be suffering and that could be the reason for an ammonia spike.

However if the pH is being kept enough above 6 that you know for certain it isn't below, then it is in the measurable range and the ammonia spike isn't due to a pH crash.  (a little point on that though, if your system cycles up at say 7.8 and then you let it suddenly plummet or you adjust it down to 6.2 in only a couple days, the bacteria is going to have a rough time adjusting and it could take several days for the bacteria to get used to the new pH and catch back up on their duties.

Any time there is an ammonia or nitrite spike, the first response should be to cut back or stop feeding then look around for possible sources of the problem.


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