With a KH that averages 5 dKH my 5lb tank lasts about 6 months.

 

With a KH that averages 5 dKH my 5lb tank lasts about 6 months.

How big is your tank?

 

With a KH that averages 5 dKH my 5lb tank lasts about 6 months.

KH has no relevance as to how much CO2 one must add. You would add the same amount of CO2 to a tank with 2 KH as you would a tank with 8 KH and so on.

A 5 lb. tank will last at least 6 months and longer if you use a solenoid and turn it off at night. I had a 10 lb. tank on the same size tank run 24/7 for a year.

 

KH has no relevance as to how much CO2 one must add. You would add the same amount of CO2 to a tank with 2 KH as you would a tank with 8 KH and so on.

I must be missing something here, Aaron. :???: I have a higher KH (9) and I have to pump in more C02 to keep my levels at a consistent rate. I use a controller, and obviously a higher KH is going to be more resistant to bringing my pH down to the desired level than a lower KH that will change much faster. I know you need a lower pH with a lower KH, but I don't think the C02 consumption has the same formulation when comparing KH. What am I not seeing? :-s

BigChuck, a 5# would work just fine on a 75 gallon and like the others said, probably last over 6 months, but if you have the means, it's much more economical to go with a 10#. Around here, Airgas only charges about $2 more to fill a 10# opposed to a 5#, and when you consider the hazmat charge per tank, you're really saving to get twice as much for the same hazmat fee.

 

I must be missing something here, Aaron. :???: I have a higher KH (9) and I have to pump in more C02 to keep my levels at a consistent rate. I use a controller, and obviously a higher KH is going to be more resistant to bringing my pH down to the desired level than a lower KH that will change much faster. I know you need a lower pH with a lower KH, but I don't think the C02 consumption has the same formulation when comparing KH. What am I not seeing? :-s

Jan,

That shouldn't be the case. For example if you have a tank with a KH of 3 and a 2 bubble/sec CO2 rate gives you 30 ppm CO2 levels then upping the KH of that same tank should not result in a need to adjust the CO2 bubble count. In other words it is not an exponential relationship. At least, this is my understanding. Someone please correct me if I am wrong.

 

Jan,

It may be easiest to look at relastic numbers, with the assumption that no other buffer is messing with CO2's relationship with KH and pH.

CO2 ppm = 3 * dKH * 10^(7-pH)

Constant CO2 from aged tap of 3ppm and 30ppm CO2 after injection:

Example 1
1 dKH
Tap pH of 7.0
pH after injection 6.0
pH change 1.0

Example 2
3 dKH
Tap pH of 7.5
pH after injection 6.5
pH change: 1.0

Example 3
10 dKH
Tap pH of 8.0
pH after injection 7.0
pH change: 1.0

HTH

 

Buy the biggest co2 tank that will fit where you are going to keep it. I have my 5 lb co2 under my 55 gallon tank. It lasts about 6-8 months. wish I had a 10 lb tank but not sure if it would fit. It often costs very little more to fill a larger tank than a small one.

Bob

 

I currently have a 15lb tank on a 37G Cube. I got mine used, but it's tested and primered (June 2005) for $36. Try asking around welding supply shops for a good deal.

 

Buy the biggest co2 tank that will fit where you are going to keep it.

I agree with Bob. Also check at fire extinguisher companies, that's where I got mine.

 

Found someone through the internet who is selling a 5# tank for 30 bucks! Picking it up this weekend! Can't wait to set this up and see my tank explode with growth...that is if I do it all right

 

Good deal, looking forward to some pics