Help with Flushing

I had a serious overferting problem, which is now the result of 2 almost dead and one starting to show problems. Yesterday I flushed all 3 plants with a gallon of pure water 6.0ph . Today i have flushed them all with a gallon as well ( 6.0ph ). I use rootS Organics soilless media which recommends a ph of 5.5-6.5 . Plants are at day 28 of flowering. I have only had the ph meter for about a 2.5 weeks so i am almost positive i had nutrient lockout and burn. When i add my nutrients ( Botanicare ProBloom and Liquid Karma ) it drops the ph to 6.1 . I use filtered water which is 7.1, my tap water is 8.5 . Hydro store recommended Cal Mag+ .

How long, and how much should I flush the plants? I've been told that soilless mixes do not hold nutrients as well as soil, so I should stay on a nutrient feeding schedule, is this true? Once they are flushed should I throw them right back onto full nutes or ease back into them?

I definately don't like the medium as it is too tempermental, definately gonna switch to FF Ocean Mix or bcuZZ. On previous grows I used all the same nutes that I am using now plus silica blast with bcuzz soil. Never had problems.....

oh yea, the pots I'm using are 6.5" tall and 6.5" in diameter at the top.

When I had to leech my soil I used three times the volume of the pot. My pots are 3 gal. so I used about 9 gal. I recently read that when you do this you shouldn't use plain water. Instead you should add a "weak form of the nutrients you plan on using". This makes sense to me because you don't want the soil to be completely devoid of nutrients. I'm not sure about organics soilless media though. I am working on my first grow and this is my first reply to someone's post so you probably want to hear from someone with more experience.