Lowering pH in Aquaponics
Many beginners and intermediate aquaponic growers are often concerned about their high pH and want a quick fix to bring it down.
This post will be short and sweet because my philosophies on lowering the pH in system with high pH are relatively uncomplicated.
Lowering pH in Aquaponic Systems
If you’re thinking about using a chemical or acid to lower your pH, don’t.
High system pH is almost invariable caused by carbonate buildup in the system (when it’s not carbonates in the form of limestone growbed media, concrete in the fish tank, etc.).
When it is carbonate buildup in the system, your pH is being “buffered,” or maintained artificially high by the carbonate cycle of your water. Carbonates can be a complicated subject, so I’m not going to get into them here, but the thing to remember is that carbonates have the ability to dissolve into solution, and precipitate out of solution in a way that maintains pH in a very specific high range until one day, you’re adding acid like you usually do, and your pH crashes. Bottoms out. Drops like a rock. When this happens this quickly in high pH systems, the first thing that happens is nitrification stops- which we all know is a very bad thing.
How to Safely Lower pH
So what are you supposed to do? If your water isn’t that hard, you can eventually get your system nitrification to the point where your acidification from nitrification outstrips the carbonates entering your system, leading to a naturally low pH. When done correctly and slowly, the nitrifying bacteria can be given time to adjust and there’s no shock. Once you reach this sweet spot in your system’s health and lifespan, it is a wonderful thing. At this point you have control of your system pH. Where do you want it? It’s completely up to you.
If your water is harder than most, or if you simply don’t want to wait, the best thing to do is install an RO filter (Reverse Osmosis). RO filters remove almost everything from the water (including carbonates) leaving you with very pure, carbonate free water.
RO filtered water is uncomplicated stuff. You can allow nitrification to drive pH down, or you can add simple hydroxides to raise pH (and supplement nutrients) with no long term pH effects. RO filters can cost a few hundred dollars, but in my experience, many of the folks who spend months struggling with pH, and artificially trying to lower it, reached the point where looking back, they wish they’d just installed an RO filter and avoided the cost and heartache of fighting the fundamental chemistry of their system.
Don’t forget about Biological Surface Area
So there it is. You have two solutions- either be patient, or drop some money on an RO filter.
If you do choose to wait, I do recommend using a growing technique that contributes lots of Biological Surface Area to the system. This increases the potential amount of nitrifying biomass in your system as well as the resulting efficiency in nitrification. This can lead to faster nitrification based carbonate consumption.
We use ZipGrow towers for this purpose because our media has massive Specific Surface Area (SSA) and really helps get nitrification at peak efficiency.
I hope this is helpful for you, and really commiserate with those of you who are struggling with this issue.
Controlling your system pH can be an incredibly frustrating task, but if you follow my advice, you can take the first steps towards taking control of your system and how it operates.