Dealing with summer heat.

I am getting ready for my grow and have been dealing with high summer temps. Does anyone know if you can use a 6/6 cycle after the plants go through the veg cycle? Also, if 6/6 is possible, will it make the plant more compact with denser buds? Planning on Fimming and LST/SCROG. I realize I may have to get an inline cooler or a/c, but was hoping to not spend more than I already have (should have just bought a completed grow box).
Using a 600 HPS Hortilux with drip hydro setup. Germing my Nirvana Northern Lights and Bubblicious right now and will transplant to rockwool cubes in hydroton. Have built a cabinet 4x4x4. Max room between hood and top of pot is about 30 inches.
I truly am grateful for all the wonderful posts I have researched on this website and hope my success is as wonderful as some of the amazing pics I have seen.
 
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