Cycle Question

I have had my 90g up and running for a little over 4 weeks now and have been testing for ammonia, nitrite, nitrate etc. and am still getting .25 or less on all my tests. I started the tank with mostly dry rock / sand and then one 20lb bag of aragalive live sand, 5lbs of live rock from another tank and a cup of sand from another established tank to seed it. After getting no ammonia for 2 weeks I dropped a piece of raw shrimp in. That dissolved pretty quickly but still no ammonia, nitrites and no algea blooms 2 weeks later. Do I need to do anything to get this started or just continue to wait. I am not really in a hurry but it seems like the tank is as sterile now as it was when I started. Tank looks awesome (minus nothing in it !!) and runs awesome otherwise. Any thoughts ??? Should I start dosing ammonia or feeding the tank?


Also, I have been running my skimmer, GFO and carbon the whole time. No lights though. Salinity, PH & temp all in normal ranges. Phosphate levels also very low. Next to 0 basically.

 

How much do I add to the tank and how often? Do you stop adding it then when the ammonia levels drop right away? I am assuming you just get the pure ammonia from the cleaning isle at hardware store or something? Thanks for the help.