First thing you should to is buy a phosphate test kit if you dont have one. Check your levels and see what your phosphates are at. If they are high, you might need to make some water changes (top-off water). Some tap waters contain high phosphates, in which case you may want to start using Reverse Osmosis water. There are some slime algae removers on the market you could try, but the easiest way is to find the cause.
Some possible causes are:
1. Low alkalinity
2. High Phosphates
3. Newly installed protein skimmer (somtimes)
4. Excess feeding (adding phosphates)
You can check all your levels and see where they are. You can try more routine water changes to help eliminate this or you could try adding a refugium with some macro-algaes which will help fight for the same nutrients as the micro-algaes and usually remove them.
HTH
-Andy