I wouldn't remove the sponge. Seeing as you clean it often, I doubt very much that it's the source of your nitrates. Leaving a skimmer off for a few days would not cause a huge spike in nitrates so either the nitrates have been high for a while, something has died in your tank, or the test is wrong. Test again when you have a minute. Also, test the output of your r.o. unit for nitrates. Do you clean/vaccuum your crushed coral at all? |