Me and My Girls need Help!

I am in my 4th week on a grow of NL's and I have been chasing a problem that started out as a few rust spots on a couple leaves on one of four plants in a Eco Grower Hydro/DWC/Drip system. The spots are now on a couple of other leaves but only a few. I could give you a history of all the steps I've taken but at this point I figured to give the experts a few basics and pics to generate comments and questions. PH has averaged 5.3 with little swings; HG Flora Series @ PPM 720 (.50 Hanna); Solution Temp 72F; Tent Temp 79F & 55% RH during Day & 69F & 40% RH during night time. I can provide additional info as requested. Thanks

Have to check here, PH @ 5.3, typo? If not you should get that back up to 5.8 avg. @ 5.3 you are going to lock some nutrients out, this looks like Ca deficiency, which at a PH that low is a definite possibility IMO. Before adjusting nutrients I'd start with PH.

Cheers,
Enigma

Also one suggestion. I tried a DWC/drip myself. Had nothing but trouble. The drip system add nothing beneficial in DWC, it will only contribute to problems in your DWC as the dripped water is exposed to light. Esspecialy with your system running hot (solution at 72 is pushing it). As you are going synthetic with the flora series are you adding H2O2 to help keep things in check?

Cheers,
Enigma