Crabs???

I'm thinking about getting some crabs for one of my tanks or do I need just a crab tank and I would like some advice on how to keep them and what tank they would be most suited to. I have one 50 gallon tank with 6 fish from 4.5 inches to about 13-14 inches and they are a kissing grouami, a gold gourami, a sailfin pleco, a red tailed shark, and two european chub no plants as yet but alots of rocks. The other tank is 20 gallons and has from 4mm(newborn baby guppies) to 2.5 inches and they are 5 pepered croy, 5 cherry barb, 5 odessa barb, 4 neon tetra, 2 danio, 2 bristlenose catfish, pair of dwarf gourami and 13 guppies well planted, bogwood and a castle.
I ether won't some taI red crab or some rainbow crab

Anything would be helpful
Thank You

 

I'm thinking about getting some crabs for one of my tanks or do I need just a crab tank and I would like some advice on how to keep them and what tank they would be most suited to. I have one 50 gallon tank with 6 fish from 4.5 inches to about 13-14 inches and they are a kissing grouami, a gold gourami, a sailfin pleco, a red tailed shark, and two european chub no plants as yet but alots of rocks. The other tank is 20 gallons and has from 4mm(newborn baby guppies) to 2.5 inches and they are 5 pepered croy, 5 cherry barb, 5 odessa barb, 4 neon tetra, 2 danio, 2 bristlenose catfish, pair of dwarf gourami and 13 guppies well planted, bogwood and a castle.
I ether won't some taI red crab or some rainbow crab


Anything would be helpful
Thank You

I think any kind of crab would try to eat your fish especially at nighttime they hunt and fish sleep at the bottom sometimes
I found some links good info

 

Crabs will find any weakness in your defences and escape from your tank.

Forget "The great escape", crabs write their own rules, jumping the tank wall on a motorcycle is not beyond them!

Every crab I've tried to keep has ended it's days covered in dust and dog hair while looking for water.

So, best advice:
1. Don't bother
2. Make sure they have an area they can get out of the water
3. They will escape so don't bother

 

The only thing that's better at escaping that a crab is an octopus

 

Thank not getting any now possible a betta tank now