In Sylvia's video on KH (http://www.theaquaponicstore.com/API-KH-Test-Kit-p/atspw014.htm) she states that the KH should not go above 18 drops. Mine is > 25 drops (Not sure the upper-bound, as I gave up after 25).
I had a calcium deficiency in my plants from being locked out from the pH being too high. Not realizing this, I kept adding calcium carbonate until the symptoms went away; hence the really high KH. While my plants don't look sickly, I'm afraid I'm limiting their potential.
Should I do water changes to get the KH back down? Or, should I let mother nature work it out over time?
What is your pH?
7 < pH < 7.6. I have been slowly adding Aqua Down (phosphoric acid), with the goal to get it under 7.
If your pH is under 8.3 (which yours is), that means you have exclusively bicarbonate chemistry. Yay. Your KH could be much higher (and i've seen such) and the pH wouldn't increase much. The amount of phosphoric acid you have to add to get it under 7 will be significant. Why not just leave it where it is?
Why would you want to leave it there when at that PH, you lock out a lot of nutrients for your plants? I've heard that in time your PH would normally go down but it's been over a year and I still have to add aquadown periodically to keep it down. Please explain. Thanks
pH is a balancing act between acids and bases. In our systems, the acid is usually CO2, the base is the KH. Adding acid burns through the alkalinity, but I assume the alkalinity comes from your source-water. So every time you top-up the system you're adding tons more alkalinity.
I'd recommend dealing with the nutrient lock-out by using chelated iron.
I have an IBC that is over a year old and the pH stays around 7.4. I have 3 smaller tanks that I have to continually struggle with the raise pH. Don't know why. It's funny that the system that I'm growing plants in stays high and the ones that just have fish are way down. I'd like to reverse that. I have heard that some media will increase pH. You might look at that angle.
Thanks to you all for the advice!
Do you think it would be harmful to do a partial water change? It might be more work then it is worth, but I feel like I've added too many nutrients to the water.
I'd ride it out and see if the pH comes down on it's own. As for using chelated iron, it might work for you but you'll never get the brown out of your water.