http://forum.aqua-fish.net/ A forum devoted to aquarium fish, plants, techniques and fish keeping as a whole. en http://forum.aqua-fish.net/?topic=need-help-#1 I have a 55gal. Freshwater planted aquarium. I have abot 10 fish right now. 4 rainbows, Couple of loachs, SAE, Otos. I have many corkscrew vals and some anubias. I have substrate that I bought specifically for the planted tank.1 piece of driftwood. I have 265 watts of compact flouresant light, 2-65watt 6700K and 2-65watt 10000K. I have a Fluval 404 with ceramic cubes in the bottom media tray, thick polyester pads in the second tray, bioblend carbon/zeolite in the third tray, and biological media cubes in the top tray. i also have an automatic CO2 system that is set the maintain a ph of 7.0 for now. My problem is that when I do a water change, my ph drops drastically. I am using tap water conditioned with stresscoat. The ph of my tap water is 7.0, GH is high normal, Kh is within normal range, nothing else shows up when testing. My aquarium water has no nitrate, no nitrite, and a ph of 6.8-7.0. Nothing changes except the water and cleaning the filter. ex. last water change, immediately afetr ph 7.0 for approx. 12 hours, then ph started to drop until I found it at 4.9. Nothing was added or taken away from the water or filter. Any ideas? wcaicedo 2009-03-08 http://forum.aqua-fish.net/?topic=need-help-#2 The only two obvious reasons I can think off are the KH being too low i.e. below 4 or there is too much CO2 being pumped into the water but from your opening post it seems that you have them covered. I take it that you are running a solenoid that closes off your CO2 at night. mickey 2009-03-09 http://forum.aqua-fish.net/?topic=need-help-#3 I have since turned off my CO2 cylinder altogether. I have raised the kh with baking soda, like I always have to do, and I am still getting the drop in ph. I am at a loss. I have tried just about everything that I know to do. wcaicedo 2009-03-10 http://forum.aqua-fish.net/?topic=need-help-#4 This is a bit of a mystery here, have you tried running an airline to dispel some of the CO2 out of the water. I noticed in your post that you have driftwood in the tank, was it boiled first before adding it or is it a new peice of wood? Do you gravel vac the substrate on a regular basis? mickey 2009-03-11