hey kat look here, i know i'm gonna get bombed on when i tell you this, but i use 3gal pot 98% of the time and i water like every 6 or 7 days. now here recently i have been water ing every five to six days on the nose, depending on how the pot feels, and it works out great. i just go by the weight of the pot. trust me over the course of a month or so you'll be able to tell by the weight of the pot, and when you want to water it. seeing that my grow is based on the cheaper scale my nutes usually go me one and a half runs. but it always last for an entire run with some left over, and that is with me increasing the amount every week.
now as far as your other query;NEVER use only water with your coco, at best use a lite A-B solution mix, trust me it just messes things up when you do that, not recommended. secondly, there are a few guys that won't agree with me, but it is ok to use regular water. TRUST ME! PLEASE! seeing your situation and others like yours as well, why would you want to purchase, load, and pack back to the house R/O water when regular tap works just as well as long as it is between 5.6 or 8 and i think 6.2. like i said if you dont believe, check my journal, post #43, i have a short feeding chart and some pics of past and present crops and harvest. so the proof is in the pudding. i just dontwant peolpe spending money they really don't have to. but hey the final decision is yours, but i invite anyone just using the A-B, and a bloom booster in r/o water under 400's with loose coco to show their's, and we can compare. but check it out.
PEACE!!!
-ZEN-