Lowering hardness

[jackdp]

In our newly setup dwarf puffer tank there is a hardness problem. The problem being that I used our tap water for topoffs a couple of weeks ago and it is very hard. Now the hardness in the aquarium is 23 degrees GH by my Aquarium Pharmaeuticals test kit. Also the nitrates are close to 20mg/l by my Seachem kit. In order to lower both hardness and nitrates, I'm assuming some partial water changes with my RO/DI water will accomplish both. Do I have to worry about the fish being affected by dropping hardness or nitrates to quickly? I'm not sure whether it is better to get the hardness and nitrates down as quickly as possible or to do it slowly so as not to shock the DP's. The tank is 15 gallons with TetraTec filter, planted and has 3 dwarf puffer and 2 Otocinculus algae eaters in it. TIA

 

[rich311k]

Actually 20ppm nitrate is not that high. The fish wont care if you chop that in half or eliminate all together. Fish are also not that sensetive to GH, KH is the worrisome one. If your KH is high as well, then you will want to go slow when changing the water.