Pardon my flaming ignorance, but what might be a RO filter?? sorry, I'm still in the learning stage
Been a bit of discussion about this lately in the pH for different crops discussion. Nate has had good luck with using an RO filter to remove carbonates and allow for tighter control of pH and nutrients.
It means reverse osmosis. It filters the minerals and most impurities out of the water. Please do not use Vitamin C in AP as it will crash the bacteria in your AP. The RO will bring your PH down to around 7ppm if you are above this value. You can use the search bar(top right) to search the site for any info you're curious about.(Also googling it helps you learn faster)
This is only one of the topics associated with topics of this kind http://aquaponicscommunity.com/forum/topics/ph-level-and-crop (TC was referring to)
I have had good success using dechlorinator i bought at the local petstore and ph down.
There can be some problems with PH down. There are a lot of products out there that will work and do what it's said to do but sometimes they won't work for Aquaponics. We've had members here that used products like the PH down containing sulphur and citric acid and both of these are not compatible with AP. I'm not saying that there aren't other products being used in soil based agriculture, aquaculture, and hydroponics that are compatible with AP use, but education on AP dynamics should be properly understood before we adopt their use.