Plain water is fine, anything else is just another way to get you to spend money on dubious products.
No need to drown your plants with gallons of water either, just give plain water, nothing else, and in normal amounts and at normal intervals for the last 10-14 days before harvest and the plants will "flush" themselves naturally.
Adding mycorrhizae to the roots when planting or transplanting is something I would recommend highly for your next grow, it is an amazing additive.
"Mykos" frow Xtreme Gardening is the product I use, but there are others, like Great White Shark etc.
Kelp tonic/extract is another excellent additive, especially for transplanting, stress situations or just as a health boost.
I am also a big fan of humic acid, fulvic acid and amino acids for plant vitality.