Re: [APD] CO2 equipment

[Andrew Mitchell <andrewm at cse_unsw.edu.au>]

On Wed, 2004-02-11 at 04:05, Bob A wrote:
> I am injecting CO2 with a high pressure system, but have been experiencing a perplexing problem.....
> I have a 125g. planted, discus tank.  I try to keep the pH between 6.7 and 6.8. KH is 5 and GH is 9-10.  
> The prob is that I go thru a 10 lb. tank in just under 3 wks!!!
> I suspect maybe a leak in my regulator, but cant find one.  Im using silicon tubing which leads into a 
> power head that feeds a reactor in my sump, which empties into the sump water and fed directly by way of 
> Eheim pump back into the main tank.  I am using a trickle, wet-dry filtration system.  No agitation of 
> the water in the main tank.  And, I keep the CO2 on 24/7.
> Am presently bubbling 7-8/sec (approx).  

By my vague recollection and estimates 8 bubbles per second on a 10 lb
bottle would last about a month. However 8 bubbles per second starts to
get difficult to count, and perhaps bubbles can be of different sizes
etcetera... so you may or may not have a leak.

Whilst a leak may be partially responsible, I'd try getting that
bubble/sec count down and reducing your CO2 losses. If all attempts to
reduce CO2 losses fail then it may be a leak issue.

After discussions with Scott H. over the last few weeks I've changed my
(immature and very very approximate) CO2 rule of thumb to...
"On a wet/dry system if you are using much more than 1
bubble/minute/gallon (at 20ppm CO2) then you could save a fair bit of
CO2 by reducing CO2 losses. If your figure is less than 0.3 then
overnight O2 content of your water is worth watching closely".
 
So on your 125g if you are aiming for 20ppm, then anything more than 125
bubbles/minute means that you are losing a fair bit of CO2 somewhere. 
You are running about 3.5 b/m/g, whereas I am (now) running about 0.4
b/m/g and 18ppm CO2, Scott runs at about 0.8 on 25-30ppm CO2  (all on
wet/drys).


If I were you, I would check the following (note: others may disagree on
some points and particularly the numbers)... IMHO...
1) Your reactor is working well, no CO2 losses there. (You've probably
checked this one already)
2) Your water return isn't overly agitating in the tank (ditto)
3) Losses in the air chamber of the trickle filter... it can be almost
air-tight to reduce CO2 losses. If you are concerned this may be
happening, you could try some kitchen cling-wrap and watch your ph for
10 hours.
4) Losses in your overflow (See Scott's post). This is quite a likely
cause of leakage.
5) Your total sump throughput need not be more than 1 tank revolution
per hour... i.e. in your case the true throughput of your sump pump back
into your tank need not do more than 125 gallons/hour. I have seen
people suggest 6 times per hour is optimal for discus, but I have also
seen a report saying that 1/6 times per hour is sufficient for
biological filtration in general. Personally I use 1 time per hour.
 Test this empirically using a bucket where the water enters your tank
rather than with the specs on the box of your pump. I don't know what
others on this list use for themselves on this figure.

Andrew

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