Originally Posted by cousinkenni

So I got a RO unit about 4 months ago and started using it to do water changes on a few of my tanks. In particular, on one of my 10gal tanks I use 100% RO water to do my 50% weekly w/c (5gal) and supplement with 1/4 tsp Equilibrium after the w/c. I also fertilize with KNO3(1/8tsp), KH2PO4(1ppm) 3X weekly and use 4ml Plant nutrition 3X weekly for the micros.

As far as I know I don't add any KH to my tank but every week the KH is back to 50ppm. When I test it about an hour after the w/c it has dropped to somewhere between 2-3 drops worth (Hagen test kit = 20-30ppm) but right before the next weekly w/c the KH has risen back up to 50ppm............Why?

Maybe this has been aswered before? Is something I'm adding during the week messing with the test kit? Do the plants actually produce something that increases the KH?

(unlike my ADA tank the GH seems to stay constant week to week)

Any information would be greatly appreciated.

Ken T.