Have been watching the pH in my aquarium very slowly dropping day by and trying to figure out why and whether I should be doing anything about it until I came home late last night having accidentally left the light on and found my cardinals rushing around laying eggs! My tapwater is quite soft KH = 2, pH 7.4. I add CO2 during the day at a rate of 10 bubbles per min (for a 240L tank) and the carbonates appear to be slowly used up all the time. The kH in the tank is currently 1, and pH first thing in the morning is 6. I was thinking of adding some crushed coral to try and stabilise conditions abit, but I'm not so sure now seeing as the cardinals seem to like the conditions. They looked like they were having a great time anyway, spawning the eggs and then immediately devouring them. Would love to try and collect and hatch the eggs, but having only one aquarium I suspect this is currently impossible. Anyone else have experience of cardinals spawning in a community tank?