Leaves curling up?

Hi all. First timer here and so far so good untill the past few days. I am using 400watt MH light, about a 75/25 mix of MG garden soil and sand. I water approximately every four days with tap-water that has set out for at least 36 hours. I figured there is probably quite a bit of nutrients in the soil so I have not given any type of fertilizers as of yet. Plants are approximately 3-4 weeks old in veg cycle. Most of them look really good but I have one that is getting yellowish-green blotches on new growth and a few others that are having some of their leaves beginning to curl upward. I initially thought that my light was to close so I moved it so that it is about 2 and 1/2 feet above tops. After some reading I think that maybe I may also be overwatering. Every 4 days doesn't sound like alot but this soil seems to really hold moisture. Possible Mg def. also? Temp stays around 80-85 and humidity from 35-60. Don't know Ph right now but tester is on its way. Any suggestions appreciated. BTW the stuff on the soil is just some sand, not mold or salt.

I had the same problem back in the day. My problem was due to heat. I raised the light a few extra inches and added an exhaust for it. My temps went down and so did the curling.
Hopefuly this work for you. Some symptoms may be similar for various problems.

try to get the temp to around 74-78, they will get better

bigtomatofarmer said:

I had the same problem back in the day. My problem was due to heat. I raised the light a few extra inches and added an exhaust for it. My temps went down and so did the curling.
Hopefuly this work for you. Some symptoms may be similar for various problems.

Click to expand...

Thanks for the input. That was my first thought as well. Newbie, so i'm a little paranoid, lol. Raised the light yesturday so hopefully that will take care of the curling problem. One of what i'm sure will be many mistakes.