so ive noticed that the ph in my 20 high community has been going down slowly but steadily, and im not sure why. i feed the tank sort of heavily (so that my cories get enough food), so im thinking that there might be high nitrates. also, ph started going down after i added spiderwood to the tank. what do you guys think it is, me being a bad fishkeeper, or the spiderwood releasing tannins? also the pH of my tap is 7.6.