I've used GH cocotek bricks before and hydrated with with ph balanced full strength 3-2-1 jacks mix and had great results. I've also gone the cautious route and hydrated and rinsed coco with 7 PH 100ppm tap water until it ran clear and then soaked what i was going to use in the same jacks nutrient to try and set the cation exchange. Both worked fine for me but I just hydrate with jacks 321 and plant now.
I've hydrated and then rinsed the shit out of GH cocotek bricks with 7 ph .2 ec tap water worth alright results. You'll keep your cations in check and not make things so out of wack if you use your normal ph balanced nutrient that you would water with to hydrate the coco, then water for the next week with higher than normal run off to help get rid of sodium chloride that's in the coco hogging your cations.
I personally don't do anything with my botanicare or cocotek bricks. I hydrate with well water, fill the pots and I will run the feed/watering schedule a day or two before I put in clones. This does all of the "buffering" I need.
I have used a lot of brick. Crack it into fabric pots. Put them in the bath, fill the bath.. soak, expand, drain, and squeeze out all of the water until you start seeing clear coming out of the medium. Then once you've got it properly flushed, mix up water and a max dose of CALMAG. PH it. Make sure that cal-mag rich water is the last thing you run through it.