I am using some cheap scotts potting soil and giving them tapwater that i leave sitting out overnight . the pots are 1 gallon.
I've finished in 1 gal pots before, there's very little room for error once they fill out. In your situation, I'd transplant into 3 or 5 gallon buckets (with drain holes of course) and add a shitload of perlite and a cup of powdered lime to the soil.
Once you start flowering, you want to eliminate stresses because that can result in longer flowering times or worse, hermies. Therefore, most growers transplant into their final containers a week or two
before flowering (I do it the day of, have to flower for 9 weeks but it's more convenient for me)
Also, stop watering everyday. Your roots need oxygen, let the pots get light before watering them again.