CO2 tank duration on large tanks?

[Bmeasure]

I have owned a 5 lb CO2 tank for a while now, and have recently set up a custom 125 gallon tank (actual water volume). I swapped the CO2 tanks out maybe 2 months ago and played around with the bubble count till I had roughly 2 bubbles/sec. Giving me around 7.3 pH. My normal pH is around 7.8, and KH about 5.4, so to get around 30ppm I should have somewhere around a 6.8 pH. I lowered the pH to about 6.9 pH (daylight....6.8 nighttime) which happened to be throwing out about 3 to 4 bubbles a sec....maybe even 5. I diffuse through a Filstar XP3 currently, which has worked better than any reactor I've ever used! I also have a custom wet/dry sump, but keep the water level high in sump to stop it from dripping much from the bottom of the bio-tower. The tower is a 5 gallon bucket, so it seals pretty well and shouldn't be losing much CO2 to out-gassing.

Basically, I'd like to know who else is doing a planted large (100 gal +) tank and what CO2 ppm you keep the water at. Other useful info would be the size of your CO2 tank, and how often you have to refill it. I'd like to go at least 2 months, preferably 3. Do all you large tank owners use 10 lb tanks?

[ben_manzella]

I have been running CO2 on a 90 gallon with a trickle filter for about 1 month. I built my own reactor that works well. I purchased a spray bar that is all the way at the bottom of the tank. I use a 10# cylinder and the needle has not budged on it. I would imagine it will last me about 6 months. I run about 3 bubbles a second. My PH is 7.0 and KH is 7 for 21 ppm CO2. By the way with your PH at 6.9 and KH at 5.4 your CO2 is about 20PPM which is good. I do not run CO2 at night. It runs for about 14 hours a day.

[Bmeasure]

I have been running CO2 on a 90 gallon with a trickle filter for about 1 month. I built my own reactor that works well. I purchased a spray bar that is all the way at the bottom of the tank. I use a 10# cylinder and the needle has not budged on it. I would imagine it will last me about 6 months.
You won't be able to tell it's running low until about 2 or 3 days before it "dumps". Mine have always read as if full until this time, sometimes 1 day is all I get (depending on the amount I'm pushing).

I run about 3 bubbles a second. My PH is 7.0 and KH is 7 for 21 ppm CO2.
Good, then my bubble rate of 4 or maybe 5 bubbles a second sound about right for my setup to get the amount of saturation I'm wanting (25-30ppm).

By the way with your PH at 6.9 and KH at 5.4 your CO2 is about 20PPM which is good. I do not run CO2 at night. It runs for about 14 hours a day.
Again, I want mine in the 25-30ppm range, and there is no way I'm turning mine off at night! I would have some questionable pH swings between early morning and late night. I don't max my output out for the reason of having a little safety margin. For instance 30ppm is 6.7 pH for me and I'm aiming for about 6.8 during daylight hours. I'd test your pH readings in early morning (before lights on) and late night (right before lights out). See what your difference is. I'm not interested in more than about 0.1 pH difference happening in my tank (which doesn't). It's about 6.88 before lights on, and around 6.96 before lights out. I'm sure it would be more profound if I turned it off overnight.

Again, does anyone have a larger tank (over 100 gallons) that you can tell me about CO2 duration on?

[ashdavid]

I have a 400g planted and i am currently using a 5kg(11lb) cylinder which lasts me about two weeks . My kh is 4 and i try to keep ph at about 6.8 (20ppm) which i do so by using a ph controler. I am planning to upgrade to a 20kg (55lb) cylinder in the next few months. IMHO 30 ppm is too much for the fish and i would turn the CO2 off at night. If you are having big ph swings then you could lower your kh to 4 or there abouts. Have you heard of Mr Amano he has some great ideas about planted tanks.

[tanker]

I have a 100gal heavily planted tank and I have a huge 20lb CO2 tank (long story--I normally use a 10lb). I have set for about 50+ bubble every 30sec. My 10lb use to last about 4 months. Just started this new 20lb in January.

Hose from CO2 tank (after the valve) goes to a "T" then to 2 JBJ reactors. I like this set-up. Have been using for about 5 years (reactors need to be soaked and cleaned once in a while---I do this when changing tanks).

My CO2 is on a timer, comes on during lights and off 1/2 hour before lights go off.