Yellow & Brown Leaves...What's Wrong?

Normally the veg cycle is simple for me, but this time my plants never seem to be happy. The latest issue is areas of yellowing and brown spots on the top, middle and lower leaves. The pics are from two different plants and I'm not sure they're suffering from the same problem.

I think it could be as simple as over watering but I'm not sure. They're on a 20/4 light cycle under T5's and I've been alternating between Jack's Classic Bloom and All Purpose fertilizer (250-300ppm @ 6.8 pH) in Sunshine #4 mix (peat/perlite). Temps range from the low 70s to low 80s with humidity between 40-55%.

Can anyone tell me what's wrong?

The way that the leaves are curling parallel to the mid rib points toward a watering issue as you suggested. How often/how much do you water? What's the soil Ph?

I water every 2-3 days but the containers don't dry out equally so sometimes a soggy container gets more water than it should. I haven't checked soil pH but this mix is supposed to be properly balanced.

Ph testers are the most important tools for growing. Imo every grower should have at least a soil test kit and a liquid test kit. Soil, fertilizer and water can all affect the Ph so there's no guarantee the Ph is correct even one part's Ph is. About the top third of soil should be dry before watering again. I'll just poke a finger in the soil and if it feels completely dry, it's time to water.

i think me and your plants can agree they want to be switched to 18/6 lighting....but thats not the problem here at all....looking at those pics the JC bible say it eithet N or K def.... so that sound like you need to bump the nute....a flush never hurths either so i would do that too,..

do you use calmag?

Nope, I just put my faith in Jacks Classic.

Ok, I picked up a soil pH tester and found out my soil is 6.0, significantly lower than the 6.5-7.0 that most growers recommend. Guess I'll use some pH up to increase my water pH by a point or so to slowly increase the pH over several waterings.

Does anyone else have a way to do it?

soil being at 6 is fine man...

It helps to think of the soil and solids as having one Ph and liquids as having a separate Ph. You can add a liquid to the soil that has a better Ph and it will mix with the incorrect Ph soil to form a Ph value between the two, but you aren't actually changing the soil's Ph much. Instead of correcting the soil's Ph, you'd be mixing two wrong Ph values to form a right one. Soil Ph is best corrected by solid Ph adjusters that continuously fix the soil Ph over time. Then you can just water normally without using it every time to change the Ph. Lime is the #1 soil Ph increaser and comes in more instant or time release varieties with or without added micronutes.