co2 and blackwater?

[mourt]

Has anyone done this successfully? I'm looking at buying a co2 kit with ph controller and adding almond leaves for the therapeutic benefits and happy fish.

From what i have read, soft water does NOT make PH swings more likely. Is this right?

[DiscusDave]

Hi,

I wouldn't bother with the PH controller to be honest. originally it was thought that PH needed to be controlled but currrent thinking is that it's better to add CO2 at a constant rate during the day and use a drop checker to make sure the CO2 concentration is in the 15-30ppm range. Overnight you MUST run and airstone to get rid of the excess CO2.

I've got a planted discus tank and I target 15ppm and have no issues.

The PH swing is the same regardless of hardness (assuming you're talking about carbonate hardness - KH) - if you increase the CO2 to 15ppm during the day, then you should see about a 0.5 drop in PH, regardless of the KH. That doesn't seem to have any adverse affects on adult - but I have noticed that I don't get the best possible growth with younger fish.

Regards
Dave

[DiscusDave]

PS to clarify, CO2 injection doesn't cause PH crash since the PH will drop the same ammount regardless of the KH, the rebound the same amount when the excess CO2 is driven off at night.

However plants and naturally occuring chemical reactions consume carbonates causing KH to reduce permanatly. This will cause a gradual decline in PH. So in a planted tank it's important to keep replenishing carbonates (KH). ADA's Brighty-K does this, so does Seachem Alkaline Buffer etc. Regular water changes may be sufficient.

[Noddy65]

Are you sure Dave?
My thinking is that CO2 will decrease the ph (one of the reasons why soft drinks are so acidic) and the drop is affected by the KH?
Another way of managing it is to use a solenoid that will turn the CO2 off at night.

Mike

[DiscusDave]

Hi,

I don't mean that the PH is unaffected, it's just than the drop is temporary since as soon as you stop injecting CO2 and start running air the PH will bounce right back again.

It's a common misconception that the drop is related to the KH - it's not. Check out chucks chart and calculator (http://atlas.csd.net/~cgadd/aqua/art_plant_co2chart.htm)

Assume the KH is 2 and the CO2 is 6ppm, this gives a PH of 7. Now add CO2 to 15ppm, the PH drops to 6.6, a drop of .4 points

Now, instead assume that the KH was 10, the starting PH would be about 7.5 and ending PH about 7.1 so again a drop of .4 points!

So in both cases the change in PH is identical. Plants do much better if the CO2 concentration during the photosynthesis period is 15-30 ppm, using a drop check is a much better way to ensure this.

Generally you'll kill the fish with too much CO2 long before the PH will drop to dangerous levels since you'd have to add more than 30ppm CO2 just to reduce PH by 1 point!

Cheers

Dave

[DiscusDave]

PS Chucks chart also show why PH controllers aren't safe. If you make the controller turn off the when the PH drops 1 degree PH, that's an increase in CO2 of 45ppm! It's way to hard to get the CO2 level correct by controlling PH. You must control the CO2 directly using a drop checker - particularly if you have sensitive (expensive) fish like discus in your planted tank. Tom Bar has some great papers on this in the Bar Report.