fungus looking thing on my leaves.

So I had my plants outside for the past 4 months, and they were doing fine, then recently I bought some lights for the last week or so of veg, and to enhance the flowering. Last night was the first night I left the light on, and I noticed yellowing of some of the bigger fan leaves and a white/greyist fungus growing on some leaves!
Would the lights have accelerated the growth of a pre-existing fungi, or might it have something to do with bringing them inside thus reducing ventilation?
I've trimmed the troubled leaves, does this take care of the problem?

Let me know if photos will help.

peas.

spidr mites, look very very close and u might see some lil dot moving ,then u know if ya got em they usualy leave like lil yellow dots all over .

Get some neem oil, the cold-pressed kind... it works great on a number of issues; fungus, mites etc and it's not harmful to the plant. I like Einstein Oil, a bit pricey but it is one of the few neem oil products that is cold pressed to preserve the active ingredient. If it's not cold-pressed it usually won't work as well. It also has a lot of other natural plant oils that help it's effectiveness. But get what brand you can afford. Most neem oil products, if not already in sprayable form, will require a bit of soap to help it to suspend in water, just follow the directions and you can't go wrong. Hell I spray my babies with neem to prevent issues and all it has done is help keep them healthy and happy and I haven't had fungus or mites in the last two grows.

Yup yup i had problems with mites and all sorts of stuff but the neem oil cleared most up for me. Give a try its worth it

Can't be sure without pics.

Check FAQ. Go to plant problems. Lots of info (with pics) to help you id and clear up your problem.