I would say to go with 6 meeki, let a pair form, give em about 6-10 months to really get to know the tank, and then add a smaller pair of convicts. I have had a similar tank using large swordtails as the "dithers", it was in a 45 gallon long. 13x48" footprint. Or you could scratch the meeki, and instead go with salvini, salvini are a great tankmate for convicts or firemouths, but it soulds to me that you lean more towards the convicts. One of my favorite tanks I ever had was a 125 with 3 pairs; 1 meeki pair, 1 convict pair, and a slavini pair. Very fun and busy tank.. but like it has been pointed out, having distinct boundries so each pair has a territory is essential. Good luck, all three of those fish are a joy to keep. And as a matter of fact, my 7 year old firemouths are my favorite fish I have kept in 20 years of the hobby.
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