How long do your FE (2kg) last? I seem to going thru gas like theres no tomorrow. This is the 3rd FE I 've had since the tank was set up in March. The 1st went in about 6/8 week. When installing the 2nd one I checked all the tubing and connections and found no leaks. This next one again lasted about 8 weeks. Again checked all the pipework and no leaks found. Today just looked at the guage and it seems that this one is now nearly empty. That's 3 Fes in 4 months - why am I using so much? Drop checkers (using 4dkh) never go beyound light green and fish are acting normally.

That's probably not too bad. How fast do you bubble it in at? I use a 6.35kg pub bottle on my 200 litre tank which lasts about 4 months. James

im just about to install my 3rd since mid april,so think its about right.im doing about 2-3 bps been looking for a pub cylinder for a couple of weeks now but cant find any local for a fair price hoping to get a 5kg fe from ebay for Â£33 inc delivery unless someone else bids on it....lol

Given up using the bubble counter, even at 2bps it barely changes the dc. If I use the water collected at the back of the Rhinox diffuser as a bubble counter and set it at about 2bps this seems to change the dc to lime green but the actual bubble counter is going crazy. Maybe I didn't take into consideration the size of the tanks when people said theirs were lasting six months. The only problem I got is that the tank is full of co2 mist swirling around the tank which doesn't people always comment on when they visit during the day. Maybe I invest in an external reactor to combat this.

The length of time a cylinder will last is affected by lots of different things, one being the diffusion rate. I used to get 3 months out of my 2kg FE on my 250lt. Sam

Just joined - hi everyone ! You can calculate the length of time your CO2 should last (in days) using this equation 36141 * (weight of CO2 in kg) / (bubble count in b/s)*(useage in hours per day)*(bubble radius in mm cubed) Use the weight of co2 in the cylinder not the total cylinder weight and a bubble size of 5mm diameter (2.5mm radius) is typical. Thus, for example 2kg CO2 @ 2b/s for 10 hrs/day will last for: 36141*2 / (2*10*2.5^3) = 231 days (7 - 8 months) To save me writing it again background can be found here http://www.practicalfishkeeping.co.uk/forum/showthread.php?t=39093

You're theory looks great, but how could you explain that no one here gets his 2Kg CO2 at 2bps above 3 months? Nothing to do with your 7-8 months math

Installed an inline difusser that's helped make it last for another couple of weeks but have given up worrying about it now that I found somewhere that does refills for a 2kg tenner.

Hi charlieh The maths is all jolly nice but I don't know anyone who gets 7-8 months out of a 2kg FE . Maybe the nano boys do. Your calculations do not allow for plant consumption or surface turbulence etc. So your maths might work on an empty tank, which is not what we're trying to acheive. As each tank is completely different, most people adjust their CO2 rate to what suits the plants they've got, so the maths goes out the window after taking into consideration different consumption rates and tank conditions etc. I get about 10 weeks out of a 2 kg FE on my 180l tank . Chris

The math he made should only depend on bps, so we don't care about plants consumption or anything of what you mentioned. The error in his math is probably due to the bubble size being different from one setup to another. I have a Dennerle bubble counter laying around that specifies its bubble size in ml and mg of CO2. If I use their data, I get the same results as the math of charlieh. Since I use an AM1000, the CO2 opening hence bubble size is probably much bigger than of what the bubble counter would give. I'll give the bubble counter a try in the next weeks. I expect moving from 2bps to 4-6 bps just with this change. I'll then verify the theorical results of the bubble counter and the real 2.5-3 months I get from my canister on a 240L low light/low growth/rare stems setup (so I assume I already have lower CO2 needs than many here)

Hi jonny_ftm I hear what you're saying, but there's no way you will achieve a stable target 30ppm, over a 2 month period, with a constant bubble rate if you have a tank full of growing plants. As the plants get bigger they use more CO2 so you have to up the injection rate. So you could probably do the maths for every different bubble rate you use during the life of the cannister, but why bother, I just change mine when it's empty . But I see where he's coming from . Chris.

I fuly agree with you. I try to trim regularely to avoid those fluctuations, but I also have to adjust my bps from time to time, sure. I also don't target a number (30ppm), just a general constant trend to the green-yellow in my Co2 drop checker. As I tested many times the whole line for leaking, I felt to ask to see if my canister life on a 240L is in the medium range of what people use. And it sounds to be so. Also, the excessive price of CO2 here (90USD equivalent for a 2.5Kg refill ) let me some shocked. I was hoping to push it 6 months at least. Now, I'll go the 10Kg industrial gas renting

Hi jonny_ftm That is seriously expensive for CO2. You'll have to emigrate I get upset when I pay 16GBP (about 26USD today) for a 2kg refill, now I don't feel so bad Hope you can source some cheaper CO2 sometime soon. Chris

Don't you just love a bit of controversy The CO2 duration calculation is completely independant of tank conditions - it takes no account of how many bubbles per second are required to acheive a certain concentration in a certain sized tank but rather how long a certain amount of liquid CO2 will last when released as a stream of certain sized bubbles. The concept is sound - same as Â£100 will last for 100 days if spent at Â£1 per day or 10p per hour for 10 hours per day but the calc is quite sensitive to bubble size. So for instance 2kg CO2 run 24/7 at 2bps should last: 4.5mm bubble - 132 days, 5.0mm - 96 days, 5.5mm - 72 days, 6.0mm - 55 days BUT you will need over twice as many 4.5mm sized bubbles per second than 6mm bubbles to deliver the same amount of gas and this would be reflected by ph and plant growth in your tank. All I can say is that it works for me - I did the maths to try and predict how long my 3kg cylinder would last when I first got it in January - so far it's still going strong at about 3bps for 10 hrs per day. The calculation estimates a cylinder life of approx 7-8 months with a bubble size of 5mm so I expect that it should run out soon a 2kg cylinder run under similar conditions should last approx 5 months and a 500g cylinder 5-6 weeks. On the whole the results seem to match other peoples experiences but there are always exceptions. Perhaps I could test it better if we could compile a list of cylinder life against co2 weight, bubble rate and on-time. Any takers ? Charlie

I think a that the main problem is the size of CO2 bubbles varrying largely from one setup to another. Also the CO2 targets and way to monitor them is not the same for all people Finally, some use 24/24h, others 8h/24, 12h/24, PH meter... But a poll with: how long would your CO2 canister last, reported as grams of CO2 /L/h would be interesting to see the trends Example in my case: 2500g for 240L tank (I don't account real volume of 150L, which plays a big role + biomass...), lasts 3 months (90days), 8h a day. It gives: 2500/240/90/8 ---> 0.01446 g of CO2 or 14.46mg of CO2 injected /L/h If anyone takes...

Hi charlieh A 3 kg bottle since January I want your tank I would also be interested to see the trends...........but until then, I'll carry on changing mine when it runs out Chris