Northern lights x lowryder autoflower

The flowers are definitely getting bigger now. I'd say 1/3 to 1/2 of the pistols are turning brown, and nearly every leaf is curled at the tips. I fed them a whole gallon each of straight tap water, no nutrients, and they turned a little yellow within a day! I'll resume bloom feed next time and then only tap water until harvest. They look close, maybe 2-3 more weeks?