So, I have been running without a skimmer and using the ATS for 5 weeks now with only one water change. I tested the water again last night still have undetectable nitrates and phosphates. (Before I started running the ATS they were also undetectable.) I clean the screen ever week as directed. One side of the screen seems to have the "black and brown" algae growing. I think I need to add more light, the water flow is above minimum recommendations.

I have noticed one colony of zoanthids started not opening up completely in the past week. I changed the activated carbon last weekend and did a 25% water change. They opened up a little more but not completely. I am not convinced that this issue is related to the changes I have made to the filtration system but I also cannot rule it out.

My question is this: Are there other metrics of success to consider besides nutrient levels we can test with our standard kits that would lend itself well to a more complete understanding of the quality of the water? In other words, besides nitrates and phosphates are there other considerations that should be observed when using an ATS vs a skimmer? If I am still not clear, in very basic terms, should I be concerned about anything else going on in the system that could adversely affect the tank inhabitants from this switch besides nitrates and phosphates?

All the SPS and LPS are doing fine, it is only one colony of zoas that is all of the sudden not doing well. However, I know they sometimes just freak out for no apparent reason.

Brandon