Backyard Aquaponics
A place to discuss aquaponics

Hey guys:)

I am fairly new to AP systems because I've only had one running for about a year and a half. I've had lots of different things grow but I've always had stunted growth and issues come up in my system. When I first started I had very high pH so as I looked into how to lower the pH RO systems seemed like a good bet. Now it seems that was able to control my pH using RO water but as I learned eventually that it removes minerals that come in handy in AP systems. I've heard of people remineralize in the water and I'm thinking that may still be an option for me but I'm wondering if the reason I've always had stunted growth is because of the RO water.

Here recently I got a kh/gh test kit and noticed that my kh was 0. I've also recently learned that a 0 KH will give me no buffering capacity so I will supposedly have crazy pH swings (this was not the case for me but that is the idea behind it).

• Aside from pH swings what else would happen if you have a 0 KH?
• What is the ideal KH for an AP system?
• What is the best way to raise the KH?
• Will using Potassium Bicarbonate raise the pH?
• What is the ideal GH and does it really matter in an AP system?

Here is a video of my plants and parts of my system.

RO water has no buffering capability. So when you add it to a system it is basically only offering dilution.
(basically same as situation would be if you add distilled water)

It has been discussed around the forum previously. (search should pick the various threads up)

And wider if you search the web - re: use of RO water for horticulture generally.
It also pops up in hydroponics where they 'rebuild' the water chemistry.

In countries that use desalination for water supplies (eg. Australia) it is normal to re-add buffering minerals etc as part of the scheme water treatment process. In Western Australia it is buffered back to pH 7.0 to 7.5 through the use of calcite pellets. Along with the usual floride, chlorine etc.

Minerals are also artificially added back in to RO sourced bottled water (RO bottled water is common in Asia).

the main issue is that although it is acidic in pH sense there is not really anything to provide a chemical reaction with.
Mostly the pH is a bit like rainwater - mainly gaseous.

You will find that RO water very quickly changes pH just by adding small amounts of things - not really conducive to stability. Imagine trying to grow plants with distilled water - similar issue.

on the converse (and in line with the subject title).
If you have high GH or KH it usually flags potential issues with Calcium and things like magnesium etc.
Thus can be indicators that your system could be subject to nutrient lockout (or at least an overload of something).
It wont tell you exactly what is wrong but it does tell you something needs attention.

Often if you are adding lots of things (Epsom Salts, Calcium carbonate/bicarbonate etc etc) it is an indication that you have gone too far. In source water, again it doesn't tell you what issue is but it does suggest that you need take a closer look at your water.

A google of some hydroponic materials will give you some insight to how it affects the pure chemistry of plant growing. They are much more involved with the chemistry of things than AP'ers generally are.

Yes RO removes nutrients so unless you're adding them back in your plants will have a tough time getting the nutrients they need.

KH is not as important in AP as it is in Aquaculture and it will usually run lower in AP than it does in Aquaculture - I'm not certain what you should have for the KH or GH. I think probably around 3 or 4 for the KH but you're trying to keep your pH down around 6.8 so that affects how well you can do. The GH can be all over the place and AP will still work but this does affect nutrient availability as Darren mentioned.

If you had pH swings along with the KH being low you'd probably wind up with dead fish at some point and it would affect the bacterial filter as well.

What happens with potassium bicarbonate really depends on the starting pH but it is usually used (along with other things) to raise the pH when you get down around pH 6.0 and it also gets spray applied in a diluted form as an antifungal agent (against powdery mildew). I use shells to slow the pH drop that occurs because of nitrification and then potassium bicarbonate to kick the pH up when it gets too low. If you use this method, keep the shells in a mesh bag so that they can be removed if necessary.

Here is an article to explain:

http://www.fishlore.com/fishforum/ph/11 ... riums.html

• Aside from pH swings what else would happen if you have a 0 KH?
Large swings in pH could occur depending on other system conditions like algae growth, feeding time, etc.

• What is the ideal KH for an AP system?
Depends on what you are trying to maintain your pH at. I maintain my KH around 17-20 ppm CaCO3 and my pH sits around 6.6(GH=300-330ppm).

• What is the best way to raise the KH?
Adding bicarbonates (and ultimately carbonates) will increase your KH. This can come from your source water as well as adding supplements like potassium bicarbonate, calcium carbonate, magnesium carbonate etc. Bicarbonates are usually safer to use then hydroxides or carbonates.

• Will using Potassium Bicarbonate raise the pH?
Yes, as stated above.

• What is the ideal GH and does it really matter in an AP system?
Depends are how much calcium/magnesium that your systems needs. I shoot for 40-60ppm of calcium and about half that for magnesium(2:1 ratio) but I am only growing leafy greens. Fruiting plants would need about twice that. Also potassium needs to be added for preventing stunted plant growth (usually causes poor rooting if too low).

Hope that helps!