Plecosterone
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Convicts will populate in no time. You don't have to separate them. Sometimes others will eat the fry but cons are some of the best parents I have ever seen. Usually the other fish in the tank will be fighting for a corner when a pair have babies. Put eggcrate on the bottom of the tank, put substrate up to the top of the eggcrate and then put lots of rocks with caves and then more substrate. The eggcrate stops the cons from digging under the rocks and making them unstable. This method works great.