Daily ph Fluctuation

[tackful]

What would be considered a normal or acceptable level of ph fluctuation throughout the day in a heavily planted, DIY Co2 29 gal tank?

[tanker]

I would not be too concerned with PH shift with CO2. I would be more concerned with adding too much CO2 (but not overly so). My PH shifts from 6.6 in the early morning (before CO2) to about 6.3 during day.

[jmhart]

Any pH swings due to co2 addition aren't of too much concern. My pH typically swings from about 6.7 in the morning before lights and co2 have come on, to 6.4 when I'm fully loaded with co2. Then, at night, lights and co2 shut off and I gas off co2 to a pH of 6.7 before the cycle starts again.

Overall, if I gas off all co2, my tank has a pH of 7.4

The real concern in fluctuating pH due to co2 is that it means fluctuating levels of co2, which, depending on the fluctuation, can lead to some series algae issues.

But, alas, that is the ultimate downfall of DIY CO2...flux.

[KarlTh]

I've regularly seen a swing of a whole point. It's soup and nuts to the fish. Another pH myth knocked on the head.

[Mgamer20o0]

lol its very hard to add too much co2 with diy.....

[Robert H]

It depends on your carbonate hardness. If you have very low KH then you will have larger pH swings with C02, moderate to high KH and the swing will be much smaller

[KarlTh]

It depends on your carbonate hardness. If you have very low KH then you will have larger pH swings with C02, moderate to high KH and the swing will be much smaller

Not so. If you look at the CO2/KH/pH charts, you will find a given change in [CO2] causes the same change in pH regardless of the KH. The KH just defines where the starting point for the swing will be.

http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

Suppose KH is 3 - relatively low. Raising [CO2] from 14ppm to 23ppm - 9 ppm difference - causes pH to move from 6.8 to 6.6 - 0.2 points

Suppose KH is 8 - relatively high. Raising [CO2] from 15ppm to 24ppm - 9 ppm difference again - causes pH to move from 7.2 to 7.0 - 0.2 points, once again.

It's a common misconception, but essentially the bicarbonate system buffers the addition of other acids; it can't buffer the addition of CO2.