^I've used sand to dress the top of the soil before, when trying to kill off fungus gnat larvae, and it effected the drainage, negatively. If I were you, I'd lose the sand, altogether. Add some perlite, if you want to increase drainage.
Yeah , it's also a good idea to stop using nutes for awhile. I use the same soil(with 15-20% perlite added), and don't give them any nutes, til the beginning of 12/12. They're about 20" tall by then, and in 3 gallon pots. When they're about 16-18" tall, I go from my 1 gallon pots, to the 3 gallon pots, leave them veg for another 7-10 days, then switch to 12/12.(the transplant to fresh soil, holds them over for another 7-14 days) The only thing I use before 12/12, is CalMag Plus. When they're close to 1' tall, I hit them with the Calmag, like once a week, and never get any deficiencies. By week 5, they're 20" tall, and ready for 12/12. I start using nutes during the first week of flowering.(the plants are approx 5-6 weeks old, by then) Vegging to that size, gives me finished plants that are close to 3' tall, which is a little taller than I want, so, I'm going to cut a week off veg(maybe 10 days). Hopefully, that'll keep 'em all under 30".
What size pots are they in right now? I don't think they need transplanted, but I do think that they are suffereng from something. My guess is nute-overload.lol I'd give them a light flush, then quit feeding them for awhile. If you get more light in there, that should get 'em the jumpstart you're looking for.
