you just need one i think because the only thing you need out of the shrimp is alittle bit of ammonia. Shouldn't make the process any faster. Could put some more live rock in the tank to maybe make it faster. And i'd test the water for ammonia about 3-4 days after adding the shrimp just to see if its put any ammonia in your water. If it has take it out and don't test again for another week then just test it again, once every week until everything is 0 but your PH at 8.3 and your specific gravity is where it needs to be.