dwc medium temps?

so my water temp in my buckets is 67 but my medium is up to 75 to 78 . is this ok or normal. room temp is 72 plants are looking really good though. should i cover tops of buckets till plants are big enough to shade them? any idea please

Covering the buckets will not harm anything. However, I would point out that you said everything is "looking really good though" so why screw with it?

You're fine. Medium temp isn't a big deal with dwc as long as your water temps stay good.