Originally Posted by
bluelagoon
Even tho your water might look clean it gets full of dissolved matter over time and when you're removing half the water each time your leaving half behind and over time it adds up. Discus health starts to decline because of all the nasty's it's immune system is up against. This is why we try to keep the nitrates low; it is an indicator. Usually if nitrates are high so is the rest of that matter. There are no test kits for DOC, but there is one for TDS that measure inorganic salts, which also builds up.