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Acidity (potential issue) please Advise

Hi forum. I run a 275 tilapia tank into 2 chopped IBC beds. Last year the system worked phenomenally, save for the rain which interupted a beautiful grow season and effectively split into two... Despite it's simplicity and LACK of certain basic things, the system worked VERY very well, fish plants and everything happy. There was visibly more algae (although not uncontrollable) and ecosystem-wise, ph was more neutral..

This year, I have made some improvements to my system, however unlike last year where my pH stayed mostly neutal, this year it has leaned toward acidity EARLIER -- Despite any changes/improvements. this acidity may be good for the tomatoes, but not necessarily for everything else. My ph was 6.6 last week and now 6.3 ish, seems to be heading more acidic. I can tell the tomoatoes are liking, but not so sure about broccoli rabe, swiss chard, lettuce and the rest- not to mention the tilapia!!

Last year my ph began a bit toward ALKALINE, and then gradually headed toward acidic. began around 8.0/7.8 and took a few months to work toward 6.8-6.6 where it neutralized. I am south of that already!! Kindly advise what changes I can make to help raise Ph a bit without disrupting too much..

ADDS/CHANGES for this year:

1) Added swirl filter. Although basic, has already made notable difference in algae growth and water clarity. Ironically, Last year water was unfiltered, greener and MORE PH NEUTRAL!! WTF?!?!

2) Added 2 NTF "tubes" for lettuce - working very good so far (much better than my "zig zag" idea from last year). Lettuce and chard heads are here - I believe they'd be growing faster if ph was more neutral.

3) Changed to much better air O2 pump - is 951 gph commercial style, instead of a two-outlet "home fish tank" style with 1/4 of that output. definitely MUCH more air/oxygen into the water, yet again, ph still off...

Despite the obvious difference in water clarity from adding the swirl filter and NFT setup, my ph is leaning acidic. I would love to know your thoughts and why, and how to correct / pull toward neutral-ish.. (LESS acidic)

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Permalink Reply by Alex Veidel on April 27, 2014 at 9:32am

Well, your system probably has a healthier population of bacteria than it did last year. Beneficial bacteria love a higher pH environment, yet produce various acids that lower the pH around them. This trait causes bacteria to essentially pave the way for the establishment of beneficial fungi, which create an environment more suitable for trees, shrubs, and other perennials (fungi produce ammonium, which is a form of nitrogen that trees prefer over nitrate, which is your veggies favorite food). So, your bacteria colony is causing your pH to lower over time. It's the way things are designed to be.

Plenty of people have success with lower pH systems; plenty of plants prefer it. However, to keep your pH at the 6.8-7.0 range, you can adjust your KH level (carbonate hardness). Carbonates act as a pH buffer, which will stabilize your water parameters and slow the decrease in pH. Potassium bicarbonate is a popular choice.

http://theaquaponicsource.com/2014/02/02/the-carbonates-controversy...

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Permalink Reply by Nick Scud on April 27, 2014 at 2:53pm

So do I just add some potassium-bicarbonate powder to my tank and/or grow beds?? I guess the simple question is how much of it, and add it to what part of system?? (can be applied to sump, instead of tank-direct, for example)..

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Permalink Reply by Vlad Jovanovic on April 27, 2014 at 6:17pm

Hi Nick (cool last name i.e gammarus...a great AP detritivore)

Alex is pretty much right on the money...but

"How much"? Will really depend on your particular and specific water chemistry...that being said, you can pretty much count on 6 grams of potassium bicarb (about a teaspoon) raising your KH (carbonate hardness) about 4 dH (degrees of hardness) points in 50 liters of water.

1 dH point equals 17.8ppm (or 17.9ppm depending on which scale you use).

So, 4 dH is equivalent to 71.2ppm of carbonate hardness. How much these ppm's raises your pH will depend on your specific water chemistry...confused yet?

So, what you want to do...is grab a 5 gallon bucket of your systems water (measure and note the pH) and then put in some known (small) quantity...like maybe a teaspoon of potassium bicarb (KHCO3). Then measure and note the pH again...and just extrapolate from there.

REMEMBER THOUGH...you don't want to raise your systems pH by more that 0.4 points in a single 24 hour period. So it might be best to play with the 5 gallon bucket and your spoon until you come to an amount of KHCO3 that raises the bucket waters pH by about 0.4 pH points. then multiply that amount by 55 (to get your 275 gallons of total system water...if in fact that is the total amount of water you have in your system)...