Ya, they are nasty little dudes sometimes. I started with 13, had an alpha male die in a freak thing and all hell broke loose after. I have 8 almost full grown in my tank right now. I have wanted to up my numbers for a while, but I had to be patient as I have about 60 dems growing up right now, lol. I have 37 in the 1-1.5'' range as of right now. When they get to around two inches, they 5-6 will be added to my main tank. The 8 have worked for a while though...
Back to topic, in a 55g u are basically allowed up to 3 species as long as they stay a decent size. Dems, like u know, need to be overstocked. Yellow labs get some size to them, but are not monsters. albino socolofi also get some size, but are not gonna get as big as the acei were going to. Its ur tank, so final stock is up to u, but you would be relatively safe adding the albinos. Just food for thought. I agree with everyone though, ur tank looks great. how long has it been setup? I have some holey rock and it got covered in algae, how does ur stay clean?