I guessed that you had water quality issues and you do indeed. 40 nitrate means that your system has problem with completing the nitrogen cycle. So, you end up with unprocessed waste in your system in the form of nitrates.
I would suggest for immediate fix, do small daily water changes. 10% a day until your nitrates are down to less than 10. Also, your pH is a tad too low. I believe that with the water changes, that will correct itself. You must use well mixed salt water that has been mixed with a powerhead, preferably for two days before doing to the water change.
You will need to tell us how you have your system set up to see what we can recommend for a long-term solution for your tank. Filters, substrate, live rock, skimmer, etc.
As I suggested before, get a baby bird feeding syringe, and see if you can your assist you clown by coaxing him to feed from the syringe (while he is still able before that growth covers the mouth).
Let us know if you are able to proceed with this, otherwise, not much hope here.