Yellow spots! Could use some help

Hey guys im new to hydro growing and two weeks into adding nutrients to my plants ive noticed some small yellow spots on the leaves not sure if it is nut burn or some other imbalance, im using the dutch master gold series the full line following the grow schedule they suggested. In a small 4 gallon tank, ppm at 550, ph 5.4 ebb and flow system 3 times a day 5 min intervals, res water may be a little cold 58 f and 5 cfl lights 2 soft and 3 day lights about 6 inches above. I ALSO SPRAYED THEM CO2 WATER NOT SURE IF THAT COULD DO THIS OR NOT. Could use some suggestions thanks.

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yeah get the temp of that res up to at least 65F...58 is a bit chilly...also let your PH go up a bit..5.4 is a little low...try around 5.8

highres4 just looked at your pics and i personally think that those look very healthy im new to hydro too going to be setting up this weekend, but i do have a couple of grows under my belt in soil and unless your camera aint showing what your talking about i dont think you have any worries

I'd let my ph come up a bit, and raise my ppms. I would be worrying about cal, mag, lockout and iron deficiencies at that ph, all of which manifest themselves by showing yellow, discolored foliage.