CM....I have to say yes on the dehumidifier. Despite what some of the books say 60% is WAY too high. You honestly want to aim for the 30's but anything over 45% can create good conditions for molds/funguses. Mold can ruin your entire crop easily so the investment is worth it in my opinion.

Do you have an oscillating fan on them? Keep the air around them moving to help prevent mold issues as well but the REAL key is your humidity and your plants' general health.

I have one running in my growroom at night.....that's when you'll REALLY see the humidity rise in the grow room.