SOG soil grow, curling leaves and yellowing?

I have fairly hard water, do u think that's what's causing this? Ive had a very hard time feeding any nutes without signs of burn. I know they are in small pots (7x7x9) but cant really give them anything. I haven't feed them for about three weeks.

How high is the ppm of the tap water? It could definitely contribute. Your plants are gonna need some nutrients. What kind of soil are you using and what nutrients? Looks like they are becoming deficient in a few areas. That's gonna be a bigger problem than the potential burn if its not taken care of soon

Haven't tested the tds but quite sure it high. Going to switch to spring water till I put in an ro filter. I am using happy frog soil with added perlite. I water every other day. For nutes I was using beastie bloom and cha ching only about an 1/8 tsp per gallon once a week. I haven't feed them for about three weeks.

Those plants need some nutrients. The increasing yellowing of the leaves shows that you have a Nitrogen deficiency.
You can feed a little bit more N but it's hard to compensate it in this stage of flowering.

The curling leaves show that they live in a hot temperature.

Room temp is around 75-77 with lights on, 60-64 without. I picked up so bottled water today. how do I move forward. should I water with nutes added or just plain water. Do I have to try and flush the build up off cal from my hard water first?

I don't think this is nute burn. In my opinion you are dealing with 2 problems.. 1 heat stress.. due the upwards curling of the leave edges.
The second problem is ventilation, i see your upper leaves show nute-burn signs while your fanleaves are yellowing. If you have a fan blowing right through or ON the canopy then theres the cause of problem nr2.

goodluck