Aquaponic Gardening

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Apologies as I know this topic has been beaten to death but I am getting results that don't match most recommendations I find. 

My issue is one of low KH.   In my 180g indoor aquaponic system i use only pure reverse osmosis water salted to 1-2ppm.    I then add 50%  Hydrated Lime (calcium hydroxide) and 50% Potassium Hydroxide to settle the PH at 6.8.

It seems stable at this PH but drifts downward over a week or 2 which seems a bit faster than I would expect from what I've read. At which point I add a little more of the base solution to bring it back up to 6.8.     Plants are very healthy.  

GH is  125ppm ( or 7 dkh, 7 drops of test solution. ) 

KH is near 0.  (yellow on 1st drop.  but shows 40 on test strip. still low )

PH is 6.8 

TDS is 1430

temp 84F

Nitrate 5ppm

ammonia 0

nitrate 0

Ok. here's the big question:   I have read that I do not want carbonates in my system which is why I do not buffer with Calcium Bi-Carbonate.     KH does not seem to be impacted at all by my 50% each of Hydrated Lime (calcium hydroxide) and 50% Potassium Hydroxide.   So, am I buffering with the wrong materials?      If not, why is my KH not moving at all? 

Trying to follow Nate Storeys' advice along with many other forum posts and web sites. but am concerned about 0 KH. 



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the best way to buffer KH in an aquaponic system is by useing potassium bicarbonate.

Thanks for the reply.   I just picked some up at the brew shop.   I guess i misread the info on bicarbonates.

So here's my adjusted, new recipe.   

all reverse osmosis water


   aquarium salt to 1-2ppm

   potassium bicarbonate to bring KH to @70ppm 

   1/2  calcium hydroxide ( horticultural hydrated lime )  and 1/2  potassium hydroxide   ( to bring PH to 6.4-6.8 ) 

    DTPA chelated iron 

Please feel free to comment on this solution.  My tomatoes, basil, and lettuce are really healthy and vigorous but I am starting on 2nd try of tilapia fingerings.     All my fish died suddenly 3 months ago.    Since, I completely drained and started over with fishless cycling and this new solution, minus the potassium bicarb.   So far so good but I was concerned about KH as described in my post. 

what media are you using?

this is where you can go ahead and add a little river rock.  I use about 30% 1/2" river rock (never pea gravel), to 70% 3/4" granite. haven't adjusted pH in over 3 yrs.


RO is really not recommended for AP.. its too naked. so we add salts, and although the fish like it, they cant handle sudden changes in salinity and can die from that too.


im all about.. fix the problem, quit paying for the remedy.   .. time and money

and im too distracted/lazy to keep up with 15 different fish tanks of water chemistry.  :-)

I use hydroton as a media.   Thanks for your rock mix.  I am going to build a greenhouse out back one day and will use rock in there. 

This is a basement hobby system so don't mind tinkering with the water.   I switched to all RO  plus minerals as as learning exercise and because my city tap water is very hard (PH 8.3) and stuffed with choramines.   Lead pipes, etc.   I did fine for a year de-chorinating  and using muratic acid to bring down the ph but it was a  major pain.     I don't have my rain barrels yet so there really isn't any other option for me at the moment for a water supply.

I tried several things such as running water through carbon filters, then mixing the waste water of the RO with the filtered to get the PH correct the water but is so hard  just a bucket of it brings the PH back to 8.   So I wanted to use pure RO, then add in whatever is needed to make a healthy system.  

I think I was hung up on not using carbonates/bicarbonates at all so was left with a solution that was very low KH.   I may try the bagged shells or someday change my media.      For today, I added potassium bicarbonate to buffer/raise back up to 6.8 as suggested instead of potash/lime and we'll see how it goes.    Today, the system is very healthy with tomatoes setting fruit and fish all happy. 

Hi John,

A kh reading is a reading of carbonate hardness, so no, your not going to achieve a higher kh reading by adding any of those two hydroxides....(since they are hydroxides and not carbonates or bicarbonates). Yes, they will raise your pH, but again, not your systems kh.

For that you'd need to use a carbonate, (or faster acting) bicarbonate containing buffer 

I'm pretty sure that even Nate at times uses dolomitic lime (which is calcium magnesium carbonate), albeit sparingly...

Thanks Vlad. Much appreciated.   Bells went off and I get it.  Thanks for the clear advice. 

it sounds like your getting there. are a few additional thoughts..


with the Hydroton, you can still add river rock.

the best dechlorinator for the buck is the Green Knight hose end dechlorinator  $70 and it treats 30,000 gallons, replacement cartridges cost $27.

...and in my opinion (and im open to feed back on this) is that the chloramine scare is over rated.

my thoughts are this.. if the by product is ammonia, and we have these ammonia digesting machines we call an aquaponic system,,, is the extra ammonia all bad? ..of course im talking about a mature system. and ideally never too much fresh water added at any one time.

I used chloriminated water for 7 years at my first place, and never had a problem. we filled a 1000 gallon tank and used it after gassing off for a couple days. I would come in to find an over flow disaster etc,, and need to fill 600+ gallons of water all at once, and still never had any issues. (PS- some say I was hit with the"Lucky Stick" when it comes to AP.. they may be correct)

the tap water's pH was high as usual (around 9) and still, the acidity of the system would drop it to 5 if I didn't add river rock. but between the high pH water and the little bit of river rock, it leveled out. ...the river rock can take a week or two to show its effectiveness, so wait a while before adding more(if you think you need it).. start at 25% ( if you really want a controlled test, use five gallon buckets with holes in the sides, set down into the sides of the fish tank, or into the media beds, and see how much rock it will take to work, or if its even going to help, before tossing it into the hydroton.)


Yeah, Rob seems to have a good "hassle free" way to add carbonates and just leave it alone (assuming of coarse the river rock you use is made up of at least some limestone [read: calcium carbonate] :) no quartz type John. 

It's a totally different approach than Nate's, and we could discuss the pros and cons till the cows come home (some of that stuff has been touch on here

there is some good stuff in there if I recall...that is if you can make it through the thread without falling asleep

I like this idea, as it seems that advise is like bung holes and some have two.  

Steve R said:

I will be putting together a detailed blog post about KH PH and how to maintain them. There is alot of horrible information out there as well as people useing hydrates and other crazy ideas so I'm putting together a detailed informative post to help everyone properly understand it better.

read It will give you a much better understanding of whats going on chemistry wise with your water. Aside from the fact that bicarbonates can be used by some plants directly, potassium bicarbonate is also a good solution for powdery mildew.

The article Steve noted is great. Thanks much. I wonder if someone could comment on the supposed "carbonate-free" systems of the Nate Storey, PhD, videos. I am puzzled by his emphatic conclusions that carbonates are BAD BAD BAD. It seems clear that there is no other way than carbonates to get KH and a stable pH. I tried to send a simple question to those folks at Bright Agrotech asking what their typical KH is for their systems, but I was sent an advertisement. It seems that they are doing a daily titration of pH to keep their systems in range, not so natural, and a pain, I imagine. Can anyone debunk this claim? Thanks.
Yep you summed it up perfectly more work for only downsides. Its a hydroponic system designed by a hydro guy and its not practical for aquaponics. I too am at a loss about his fear of carbonates.

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