Yes it could be mould or fungus. I it were still green it would be trying to grow more roots. Water temps are most likely too high,very important. Larger leaves turning yellow at maturity is normal. Burning on top may be light or too much nutrients. Looks like over nutes

Very nice though just tune in your grow and maybe higher ceiling. They look like sativa, maybe indica next time ,it won't get too tall. It's all about learning and tuning in.
Enjoy the bud and next time start a mother and have all females.