Neolamp. multifasciatus in a 20H

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I had a small group of multifasciatus (6) that i bought when they were small and have grown into 3pairs, would have been pretty lucky if it was some other fish but not the best ratio for these guys is it? Well anyways, i had them for a little while in a 55gal w/ some small juli's and they multi's breed for me often just the fry would allways seem to just "disapear" so i decided to give them a tank of their own a 20h. It's been a few weeks and eveybody is starting to settle in and there is NO aggression between males, actually the tank is divided into three now and a pair is in ea. section. It took them less than a week to carry all the shell and such into 3 piles, and pile sand up inbetween. Only thing is the fry have stopped coming completly. Is this maybe because it's too many multi's for a 20 high? Or do they just need a little more time in general. I want them to bred and all but i'm not TOO worried about hurrying up because i know once it starts while there in a tank by themselves i'll have plenty of fry vs. the one or 2 that would survive in the community tank. I just want to know if considering my 1:1 ratio if 6 multi's is just too much for a 20h.

thanks
-matt
oh and i would be removing older fry to my fry tank so i wouldn't be allowing too much of a population growth to happen