Just another warning about making changes to c02 and making sure you stick around.
I have a 75 gal rimless with a magnum 350 to filter it. Using a diy nw rio 1k in tank for c02. Nice mist and not a huge bubble rate (for me at least!). PH drops approx .75 within an hour. Fish seemed fine.
I planted some HC yesterday and also increased the NV bubble rate a tiny bit. Stuck around all day but had to work late last night and into the early morning. I live across the street from my job, so I came home a couple times to check on this. Sure enough, the 2nd trip, the 20 cardinals I had were all at the top gasping. C02 had been OFF for 2 hours at this time!!!!
Note that the ph decrease was from .76 to .79 tops. It has not increased past that when I saw the fish in distress.
I attribute this to the use of the canister which traps c02 longer term along with Tom's observations about the non-linear response of ph and c02 ppm. I saw this with my 220 before I swapped to a large wet/dry. Thing is that I provide LOTS of surface movement now, much more than most folks provide. I even increased it simultaneously with the small c02 increase!
So, I provided plenty of surface agitation and within 10 minutes things were better. However, I think I lost 3 cards.
So I urge you all AGAIN. When you make ANY changes to c02 you need to stick around and monitor. Even after c02 is off.
I will be watching more closely today and I turned the rate back down to the previous level. I will provide even more surface ripple.