What color / type is it? If its red slime cyano
from over feeding etc... it can just be siphoned or vac-ed off the substrate and even off the LR
... I'd test your water and do some water changes etc... clean your glass up good and even add a nice size clean up crew too
Glad your fish made it
I had my husbands cousin 'watch our tank and well, I didn't have timers, we were gone 4 or 5 days and he never came ONCE... my lights were on 24/7 and I had a huge neon green tank.. my fish made it too... I was shocked, as I couldn't even see thorugh my tank when I walked it.
Welcome back BTW