Water quality

Question
To All;  I have had a 37 gallon saltwater tank for several years.  I have just recently converted to a 75 gallon tank with a canister filter.  I moved all of my live rock (about 40 lbs), all of my water, corals and fish.  I topped the tank off with spring water and instant ocean.  It has been about 6 weeks now.  Over the six weeks I have added some inverts, more live rock, some corals and have attempted to add a total of 4 fish. (one at a time)  most of my newly added inverts and all of my newely added fish keep dying.  My tanks Nitrates are still high and I have a film on the top my water.  My filter is a RENA 3 (built for a 175 gallon tank) I have a protien skimmer for a 100 gallon tank and an additional power head.  I also have powercompact lights.  What could be going on?  My corals are doing wonderful except for my stony coral (chain daisy) I'm lost ?  Please help.  

Answer
What are the rest of your water test levels?

The film on the top of the water is typically associated with gas built up in the tank from a lack of surface aggitation.  Redirect one of the filter outlets so that you get more movement on the top of the water and see what happens.

Also, if your skimmer is working correctly you really shouldn't be seeing that type of thing.

This lack of gas exchange can cause CO2 levels to rise in the tank effecting pH and clearly holding back oxygen levels.  Not as big a deal during the day when algaes and whatnot are photosynthesising, but at night... your pH can drop pretty low and your oxygen levels can get dangerously low.  Could be why your losing fish.

I'm curious to see what your ammonia and nitrite levels are like.  High nitrates are the least of your concerns right now, however, if you are looking to lower those levels I suggest consistent water changes with reverse osmosis filtered water over the next several weeks until the desired level is achieved.

Best of luck with your tank!

Regards,
Scott Johnson
Aquarium Crazy Fish
www.aquariumcrazyfish.com