but im thinking of redoing my 90 as saltwater and trying to grow crabs (prefer alaskin kings) or lobsters for obvious reasons dont know where i would buy them or if i could do it any help greatly apreciated
i think it would be pretty impossible to get live alaskan king crabs. Aren't they pound for pound, the most expensive invert. you can get. Fishing for them is also one of the most dangerous jobs on the planet. I'd say to just get some really nice looking fish and buy the crabs and lobsters at your supermarket.
Nic, you will need serious chiller for a 90g, kept indoors you are going to need something that will give you a forty degree F. drawdown. That would buy a lot of lobsters, if you go for a large edible invert try spiney lobster or stone crab, they are warm water. Or stick with freshwater and get a giant Tazzie crayfish, they get something like 2+ pounds.
If you want to go for SW lobster size you could try raising a Tasmanian giant crayfish (Astacopsis gouldii). They grow to 12 pounds and records have bull males hitting the 20 pound range. They're warm-water crays so you won't need the chiller. The only major drawback is they're available only from a gov't research lab that allows only a few sold each year. And, they want $1000.00 (plus quarantine, customs, shipping, etc) for 3" juvies.
The most readily available species of large warm-water crays is Cherax quadricarinatus (red-claw crayfish). This species grows to about 14" and can weigh up to just over a pound.
Here's a pair of mine. The male is on top (red patches on the pincers). The female is carrying about 400 larvae.