Hi, I have been building up my cardinal school in my 55g. I buy 10 at a time, 15 if they are very juvenile, and quarantine them in a 10g tank. However, the QT is well established with two small internal filters with additional sponges over the inlets, increasing the media surface area many times over. It also has a lot of plant and moss in the tank. In the first few days I water change 20% a day until I'm sure the filters have caught up with the extra bio-load. Then I change about 20% twice a week. I like my QT and enjoy having some fish in the tank so keep them for a minimum of 8 weeks, but is is excessive. What I can say is that 2 weeks for cardinals is not enough for some illnesses to show, neon tetra disease being one of them. I have had weak fish showing signs as late as 3 weeks after introduction. 4 weeks would be my minimum.
I put all10 into my display tank at once, after a 20% water change, test the water daily, treat with Prime if ammonia or nitrite even remotely rises and change water accordingly. The display tank filters have normally caught up after a week.
The end result is well worth the effort.
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