It’s ok to use but I wouldn’t spend money on it. Deuterium is 1 of 2 stable forms of hydrogen. It’s not very abundant in water so it’s not something I’d be concerned about removing.

Probably too high of a calcium to magnesium ratio. Too much calcium is an issue. Cut out the cal-mag and see if it improves. If Interveinal chlorosis (magnesium issue) continues, add 1 tsp of Epsom salt per gallon of water to your base nutrients (Canna).

10-11 hours of light in flower and about 16 hours to keep light schedule in veg. Flowering plants are fucked without intense light but you can keep plants vegging under low light for 10-14 days.

I got a 4×4 with a 4” but it’s a veg tent so I use no filter. I got 5x5s with 6” in-line size fans. They work wonderfully to get negative pressure in the tents. I never used a carbon filter but once and it worked beautifully. So much so I took them off lol