Quick Question

[Benauld]

I've been toying with the idea of setting up some sort of DIY CO2 system. However, before I do this I'd like to know the following:

Is the drop in pH associated with CO2 continuous, (i.e. pH will continue to fall the longer you use CO2, potentially from neutral to very acidic.) or, is it a discrete event, (i.e. the pH will drop by X amount and only that amount regardless of how long you run the CO2 system.)?

If the former, would weekly water changes provide enough of a buffer to prevent a chronic pH drop? BTW my water is quite hard, with a GH of 18. I don't yet have a KH kit, but will be investing in one soon.

Any help would be really appreciated,

 

[Underwurlde]

The latter. There is a direct relationship between CO2, KH and pH:

CO2 (ppm) = 3 x dKH x 10^(7.0 - pH)

Usually people aim for about 30ppm.

Note, don't fall under the assumption that the above is a two way relationship, i.e. don't assume that by 'fiddling' with either pH or KH (or both) that you will 'make' CO2.

Also bear in mind that KH is notoriously difficult to measure.

Regards,

Andy

 

[Benauld]

Thanks for the reply Underwurlde.

However, I have another question now. How long do reactors/diffusers/bubble ladders keep the bubbles submerged for? The reason I ask is that I cobbled together a DIY CO2 system at the weekend, (2L coke bottle, silicon tubing, yeast and sugar solution etc) and at the moment am delivering it into the tank via a powerhead.

[I know this isn't an ideal set up & will be looking at getting some sort of external diffuser/reactor when funds allow!]

However, the powerhead does seem to mince up the bubbles really well. I'd say at least half are tiny (microscopic almost) and are directed vertically downwards on quite a strong current. The contact time for these bubbles, (on average, and as best as I can tell) is well in excess of 1 minute. I was just wondering how this compared with the contact time for manufactured kits?

 

[Underwurlde]

You are not talking like for like really.

The large bubbles produced directly out of the end of the hose has a relatively small surface area, therefore it is desireable to keep it submersed for a while (I guess the bubble ladders keep each bubble submersed for about 3 to 5 mins). The reactors, however, mist the CO2 thus vastly increasing the avaiable surface area and hence no need for a ladder.

The most efficent method is to convert a powerhead into a Venturi Reactor..... have a read through these:
http/www.barrreport.com/articles/41-diy-...-co2-users.html
http/www.barrreport.com/articles/72-venturi-design.html

Andy

 

[Benauld]

Thanks Again for the reply Andy,

However, I have yet more questions! Sorry!!

Firstly, I have ordered a ceramic diffuser, but I'm a bit confused. As stated above I'm running my CO2 in currently through an existing powerhead. Now, can I run the diffuser and the powerhead at the same time, or is that just undoing my good work by driving off CO2? (I would like to keep the powerhead to improve oxygenation and circulation of the water as my tank is deep.)

Secondly, since I started adding CO2 I've noticed that my flake food doesn't become water-logged and sink through the water column any more... does CO2 alter the water properties in any way which would cause this, for example by changing water surface tension etc? (Not that it's a problem, I just dunk it after a while.) P.S. Has anybody else noticed this?

Thanks,

Ben.

 

[Underwurlde]

IMO, using a powerhead with CO2 & diffuser should be fine. Things like airstones that cause excessive surface agitation may be a problem. Powerheads I think should be placed in a manner such that they 'gently agitate the surface of the water'.

As to any possible link between CO2 and the bouyancy of flake food, I have no idea!

Andy