CO2 - Tap, Day & Night Level Question

[jagillham]

Hi,

I’m still trying to find my way around with the CO2. I’ve calibrated the pH pen yesterday, and then found a surprising (to me!) result.

My tap water is hard, and once allowed to settle is 8.4. I’m injecting CO2 2pm to 9pm (lights 3pm to 10). The tank is around 450 litres, with a sump.

I was expecting my CO2 injected tank to be same as tap once it had gone off, and some time allowed for degassing. But, it was actually 7.8 when I measured at midday. By 5pm it had dropped to 7.5.

I’m not sure if I’m supposed to be aiming for a 1 pH drop from tap levels, or from my overnight levels?

Thanks

 

[Kezzab]

The drop is from whatever your tank PH is, not your tap.

 

[Zeus.]

I take a glass of water from tank, wait 24hrs for it to degas then take pH, repeat a few times, take average then use that figure as my baseline pH. Tap water can have quite a bit of dissolved CO2 in it.

 

[jagillham]

Thanks both, the tap is 8.4 after settling 24hrs - comes out about 7.2.

@Zeus. I’m assuming these readings you’d do pre setting up the CO2?

 

[sparkyweasel]

I was expecting my CO2 injected tank to be same as tap once it had gone off,

There are other factors that can affect the tank pH besides the CO2 level. It's not unusual for it to be different to the source water, tap or whatever.

 

[Sammy Islam]

Hi,

I’m still trying to find my way around with the CO2. I’ve calibrated the pH pen yesterday, and then found a surprising (to me!) result.

My tap water is hard, and once allowed to settle is 8.4. I’m injecting CO2 2pm to 9pm (lights 3pm to 10). The tank is around 450 litres, with a sump.

I was expecting my CO2 injected tank to be same as tap once it had gone off, and some time allowed for degassing. But, it was actually 7.8 when I measured at midday. By 5pm it had dropped to 7.5.

I’m not sure if I’m supposed to be aiming for a 1 pH drop from tap levels, or from my overnight levels?

Thanks

If you do not get back to ph8.4 before the CO2 comes on the next day then that means your tank hasn't degassed the CO2 overnight, but it depends what your tank sits at without CO2 as if you have aquasoil it could be buffering your PH and KH a little

 

[Zeus.]

the tap water is 8.4ph after settling 24hrs

the tap water comes out about 7.2pH

Which IMO/IME is about normal.
But its the tank water that we are testing.
For example here's two things that change the tanks pH
(a) many rocks in aquariums contain CaCO3 which will dissolve into the water and increase the pH esp if the water has a low pH to start with
(b) ADA Aqua Soil (ADA AS) lowers the pH of the water esp in the first few months.

Water is complex and interacts with many things in our tanks, with this in mind I would advise to take a water sample from your tank the day after a Water Change (WC) as the water straight after a WC will not be a typical day as it may not have had time to interact with (a) and (b), I use a clean glass and rinse it seral times in tank water 3/4 full, then leave it overnight at least then take pH note it down, then keep taking it every hour or so, when the pH stops changing that's the baseline pH. It might not take 24hrs mine don't, but 24hrs is easy as you take a glassful when feeding fish or daily maintenance at the same time daily (I do) so 24hrs just fits nicely IMO. Then rinse water in tank and repeat at least once.