JUST TO UPDATE:
I receive the 20" canister last weekend and has been using it for couple of days. The added air release button is a requirement for 20" as i will not be able to turn it upside down inside the stand.
I add the bypass line with valve, and leave the one to the cerges line without valve as limited on space to manouver the tubing.
with 2217, I don't seem a need to open the valve on bypass line (or use the bypass line at all) as i really see less/unnoticeable micro bubble return into the tank. Perhaps later if i use bigger filter flow (or if the bubble noticeable after filter maintenance), i might use the bypass line valve. So i decide to leave the valve as it is.
Performance wise compared to ISTA max mix large, is much better.
I can push more CO2 faster (my fish showed a little stress with the cerges in place, so i backed out on BPS) and giving a rest to the solenoid to operate less time (monitored through PH controller).
The DC (4dKH+Bromo) showing YELLOW at 6.1/6.2 mark on PH controller within an hour or less (using ISTA, i have to turned on 2 hour prior light on -- and not even got the YELLOW).
I will monitor for a while using the cerges setup to see if i need further improvement to dissolve CO2.
Thanks Guys for the advice ... !!!
This thread is really helpful ...