High RH question

Swim is growing in a closet. 3 plants under srog with 250w hps, 1 fan under scrog blowing up toward light and 1 exhaust fan with passive intake in the floorboard of closet. Plants are in week 5 of bloom so probably have around 4 weeks left before chop.

During night time (lights on), temps are between 22-24 degrees celcius (71f to 75f) and RH is roughly 47% to 55%. Both fans run during lights on.

Problem is that its winter and day time temps(lights off) is 10-15 degrees celcius (50f - 59f) and the RH is between 70% and 90%. With temps this low during daytime, even with the high RH, could mould still grow? Both fans are off during this time. Closet and room gets up to 90% RH.

If swim runs fans during lights off would the cold incoming air shock the plants? Also would it lower RH? should swim run the small circulation fan maybe and leave the exhaust off?

You really need to invest in a dehumidifier. You can then control the RH, and raise the temps a bit in the “off light” hours. Well worth the investment.