75 gallons - single fish or species only set-up

And... GO! ... trying to figure out what to put into the aba's old tank.. biggest rule... it can not outgrow the 75. prefer a solo fish or a species only... so far pondering a wolf fish of some sort.. or a group of gulper cats... I have 2x emp 400's for filtration heaters ect... atm also has potted plants which i'm splitting so either they can stay or be moved... Its next to our pool in the basement so I want to go with something "different" Our aba has been a great fit for hat but he's ready for a bigger tank and the 75 would just go into storage if I don't fill it. So something that's on the easier side of upkeep ( ie isn't a very dirty fish) would also be a plus.. but kinda not coming up with that " Omg that would be awesome!" Otherwise despite it being plenty of room i'de get a pair of something like convicts to produce feeders for the pool and the aba if we didn't just break it down ( dirty shame imo)

We have plenty of big fish.. now I want something smaller but unique.

Oh- and my husband has expressed his interest in cichlids so I might be willing to give on a single tank-banger ect.. but it has to be something spectacular..

We already have a community tank upstairs w/ a spiney eel, pair of blue rams, cory's and some teteras...

The Caquieta's are both very unique looking to me.. never seen them before. but says the males get 12" and the females 10"... not sure if that's going to end up being too big for the tank.

w/ cons and the HRP's would separating the pairs really be neccisary or are they going to pick off eachother fry?

Kevin I've considered doing something similar to the tune of mudskippers.. but I'm not sure I really want the upkeep on something like that. and def don't want anything that's going to outgrow the 75... been growing out fish for the last 3 yrs... ready to have a tank be a fishes "final tank" and not have to worry about how we're going to fit it into the house ect.

Tropheus are pretty cool, I saw a colony of "firecrackers" that caught my eye a few years ago... could they be housed with an elipisifer or Plagosi? or are they too aggressive for those eels? If that was the case my husband could get his cichlids and I could finally get my tang eels...