Aquaponic Gardening

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Brand new to aquaponics but no stranger to keeping fish of all types. 

Started my 50 gallon flood and drain system with a 6 cubic foot grow bed about 2 months ago.

Did a fishless cycle.

All went very well until I decided to change out my grow bed. I started with a 4" PVC pipe type bed with 21 3" planters. So the system was running with no plants for about 5 days until I got the new bed up and running.

After switching nitrates spiked up to about 120 ppm. I've been doing small 10% water changes for the past week and managed to get it down to about 30 ppm. Unfortunately, I think the high nitrate levels killed my ph buffer. Having trouble maintaining ph.

For the record there are about 40 gold fish in the tank ranging from about .75" to 1.25". I realize this is a bit over stocked (that's a story for another day). 

The water I'm using has a kh of 10 and a true ph of about 7.8. (After being bubbled out for 24 hours)

The tank has a kh of 0 and a falling ph that swings from 7.2 down to about 6.2 overnight.

After I do my 10% water change (doing my readings after about 24 hours) I have a ph of about 7.2 and a kh of about 4.

This lasts about 24 hours then back to ph 6.2 / kh 0.

As of today:

Nitrates are about 30 ppm. Ph 7.2 / Kh 4

I plan on doing a few more water changes to get the nitrates down below 20 ppm and hope the Kh will stabilize.

Any suggestions or info would be much appreciated.

Fish are doing fine but plants are looking a little wilted. 



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Hi Mike


It's interesting how much your nitrates spiked when you had no plants. 120ppm shouldn't cause a problem, and should be naturally used up by plants over time.  I have been told by an expert it can get to 200 without any issues. Mine went to 80 before I accidentally managed to almost completely drain my fishtank when adding a new growbed. (I noticed just in time to stop the fish from dying...).

I'm running an aquaponics research project to try and find out  how they work in practice, where you can keep track of your pool chemistry, system changes etc on-line (web, or smartphone). You can then view other people's diaries and see what others are doing. There seems to be more variability in pool chemistry than recommended with no apparent ill effects. A quick look at some of the diaries, and many are over 20 at least at times.

Anyone joining can view the diaries of other people so that can do a comparison. You may want to join this, and use this to track how your system is going, and see how others are working, and help the aquaponics community. Who knows what we can find out. The site is on



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