sykofrenic;2912023; said:
i had a crayfish in one of my tanks for a while and it tore up ALL of my plants and attacked my fish (pbass). so be aware that they can be little *******. and they eat meat too
Not attacking or disagreeing, but this is why it's important to study various species before acquiring them. Not all crayfish tear up plants, not all crayfish attack fish, not all crayfish eat meat, etc. A lot of issues with crayfish come from the fact that species that should be kept alone in tanks are forced into community settings or vice versa. Or that proper tanks aren't set up for species that require very specific environments and conditions, which can result in abnormal behaviors or death.
To the OP: A 20gal is suited for a variety of crayfish, be mindful that some of the favored Aussie species that are commonly sold will outgrow a 20gal easily. Most NA species, on the other hand, will do fine in them. However, a lot of NA species are very fish aggressive and would not be suited for your tank (2 of the most commonly sold ones, P. clarkii and P. alleni, for example are very fish aggressive and prefer meat matter over vegetable. They'd probably beat on your fish and could potentially kill them). I believe Tri-Colors are omnivorous, yes? If the crayfish had offspring they may become food for them, but I'm not sure, since I don't keep Tri-Colors.
If you want a crayfish I'd suggest getting Cherax quads (these will require large tanks as adults), O. virilis, O. limosus, Marmorkrebs, Cherax sp. Hoa Creek, etc. These are more passive species... not that casualties can't occur, but they'd be less likely to.
But if you don't know what species you're getting, general rule for safety... crayfish = species tanks, not community.