I have a 29 gallon aquarium with Eco-Complete substrate, planted with both an on-back filter as well as a sponge filter. My tank has been setup for about 1 1/2 months with weekly 25% water changes, and seems to be fairly well cycled with consistently 0 nitrites and ammonia, and nitrates maintain between 10 and 25 ppm. I use the Aquarium Coop test strips for daily testing. However, I am consistently getting low KH (40 ppm or less), pH about 6.8, and my water is hard with GH consistently between 150 and 300 ppm. I want to elevate my KH to the moderate range of 80 to 120 ppm, but I am concerned that using crushed coral will also increase the hardness even more. My plants seem to be thriving, as do the fish (after losing my 2 male guppies and 3 otos over the last few weeks. I have minimal algae. So, if I add crushed coral to elevate the KH, will this make problems for my already hard water aquarium? Or, is it best to add the coral to my filter? Thanks!
