Wanting to "renovate" my tank

[jkhudson]

I am feeling the need to change several things about my tank and need some advice on the changes. I am wanting to add some live rock, about 50 lbs. worth, and wanted to know how the loss of water volume will affect my corals and fish. Also, my cleaner shrimp and peppermint shrimp have disappered, and I think my crabs are behind it. I have no fish or corals that are predatory on them. What else could be doing it? My water chemistry is good and I add iodide 2-3 times a week. My system is a 75 gal. with 50 lbs of live rock.

 

[anjhof]

obviously the less water you have in the tank, the easier it is to change the water parameters with things like water changes, evaporation, etc...
Adding 50 lbs of live rock will probably take about 10 gallons of water out of your tank. You could tell for sure by measuring how much water you take out while adding the rock.
Depending on where you get your rock from, you might have a negative impact on the water quality, due to the life dying off the rock. You may want to add the 50 lbs. of rock in smaller increments.
I can't imagine a hermit crab taking out a cleaner shrimp or a peppermint shrimp. Do you test for iodine? IMO, if you do water changes, most supplements, including iodine are totally unnecessary.