Need to verfiy if this is a moist stress leaf problem

Hello everyone I have here 9 plants there OG cross with purple kush that i purchase from Ontario Seed Bank. The plants are 26 days old and I having an issue with the leaves.

I'm using tap water with a mild solution of Dyna Grow the label says use 1/2 Tsp per gallon my Res is 20 gallon. That would be 20 Tsp for 20 gallons I only use 15 Tsp im not sure if that the problem my leaves have gold and brown spots but the new growth looks fine and also I'm having leaf curling.
The PH is around 5.5 to 6.0 I dont have a digital PH meter just the bottle tube chart. The light is JR 250Watts that on 24/7 and grow media is hydroton and is water 4x in 24 hours (ie. 6am, 12pm, 6pm, 12am)
What do recommend me do thanks for the advice everyone
also the temps stays at 75 to 80 all the times

I don't know about you but if the label says 1/2 tsp per gallon and your useing 20 gallon res, than you would only add 10 full tsp's. So by your math you are useing 5 tsp's to many.

bigman4270 said:

I don't know about you but if the label says 1/2 tsp per gallon and your useing 20 gallon res, than you would only add 10 full tsp's. So by your math you are useing 5 tsp's to many.

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Bigman thanks for the check in but i made a error on the info i provided my wife just stated to me that she used the 12 gallon Res and that the instruction read 1/2 TSP per gallon she put 12 1/2 TSP nute.
I think it makes sense 12gallons 1/2 Tsp per gallon = 12 1/2 Tsp.
But why would the leaves curl up that why im using hydroton and i know i have to feed 4x day but my timers is the manual one with 1/2 hour on triggers would that be an issue or need to geta digital one if so who long to run pumps thanks everyone