CO2 Scrubber and PH question

[Dkmoo]

Hi All

my tank has had low ph around 7.7. Alk i try to maintain 8 - 9 dkh and i dose 1 dkh per day. last week i switch from dosing bicarbonate to dosing soda ash which temporarily increased PH to about 7.9 after dosing but returns to 7.7 the next day. Yesterday I got the BRS CO2 scrubber and installed it as a "recirculating" set up. So far i have not see any noticeable change to PH. I have a 29G +10G sump. about 25G of water volume. PH is tested at noon for the before/after comparison. I have a few questions hoping for some input:
1) how much PH increase should I be expecting with the tank size?
2) the in/out tubing on the scrubber has ID of 3/8 inch so i had to use an adapter to connect to the skimmer's 1/4 ID airline. The skimmer is a Reef Octo rated for 50G. is the skimmer too small/not enough air exchange for the scrubber to be effective?
3) there's a lot of condensation on the "in" tube since it's recirculating the air out of the skimmer - is that a cause for concern since i think the CO2 media said it shouldn't get wet?

have not seen the media change color yet (the 2 little fish CDX media)

Thanks

 

[GillMeister]

I'm running a co2 scrubber as well. I do see a measurable bump in pH that seems to last only several days. I recently changed my skimmer to a larger Bubble Magus. This new skimmer has a feature i didn't have on my old Kent Marine skimmer and that allows me to govern the amount of water it processes. I

When I started this new skimmer I kept the DC pump at about 50% and kept the water gate nearly closed to control the microbubbles. My pH leapt from 7.8 to 8.2 in a day and didn't dip below 8.1 for 2 days. After the skimmer seasoned in I cranked the pump to 85% and opened the water gate. PH dropped to 7.9.

2 days later I turned the pump down to 50% and restricted the water flow again and the pH climbed to 8.2.

What I'm seeing here makes me think the air contact time is the most important aspect of pH control with a skimmer. I'm going to see how long this maintains and if it holds up I'll post some charts.

 

[Yates273]

You can try more surface agitation which may help with ph. You will get moisture if you recirculate but try to put some kind of “catch can” to prevent it from making its way to the scrubber. I used a BRS mini reactor as my catch can.

 

[Randy Holmes-Farley]

I'm running a co2 scrubber as well. I do see a measurable bump in pH that seems to last only several days. I recently changed my skimmer to a larger Bubble Magus. This new skimmer has a feature i didn't have on my old Kent Marine skimmer and that allows me to govern the amount of water it processes. I

When I started this new skimmer I kept the DC pump at about 50% and kept the water gate nearly closed to control the microbubbles. My pH leapt from 7.8 to 8.2 in a day and didn't dip below 8.1 for 2 days. After the skimmer seasoned in I cranked the pump to 85% and opened the water gate. PH dropped to 7.9.

2 days later I turned the pump down to 50% and restricted the water flow again and the pH climbed to 8.2.

What I'm seeing here makes me think the air contact time is the most important aspect of pH control with a skimmer. I'm going to see how long this maintains and if it holds up I'll post some charts.

IMO, reducing the water flow is impacting the process in some way other than just the pure bubble contact time. Like air flow or bubble size.

Air contact in a skimmer is important for gas exchange, but the contact time for any given bubble is not important. There is no process that takes time to get going. Gas exchange does take time, especially for CO2, but you do not want to be Increasing the contact time for a given bubble, at the expensive of the number of bubbles. That would actually be counter productive.

Total air water interface at any given time, and the "freshness" of the air in contact with the water are what matters. Any process that is going to hapen happens in a tiny fraction of a secodn. then another tiny fraction, etc. Over and over, with an ever decreasing effect as the air approaches equilibrium with the water. Bubble size will have a massive effe3ct on the gas exchange rate. Smaller bubbles will be faster.

What you want for the optimal exchange rate is the biggest gas difference between the water and the air, and the greatest surface area possible. Reducing the air flow would not, for that reason, result in better gas exchange unless it impacts bubble size. More air flow would have the same total "contact", but would be more fresh at any given time.

 

[GillMeister]

Air contact in a skimmer is important for gas exchange, but the contact time for any given bubble is not important. There is no process that takes time to get going. Gas exchange does take time, especially for CO2, but you do not want to be Increasing the contact time for a given bubble, at the expensive of the number of bubbles. That would actually be counter productive.

Total air water interface at any given time, and the "freshness" of the air in contact with the water are what matters. Any process that is going to ahppen happens in a tiny fraction of a secodn. then another tiny fraction, etc. Over and over, with an ever decreasing effect as the air approaches equilibrium with the water.

What you want for the optimal exchange rate is the biggest gasdifference between the water and the air, and the greatest surface area possible. Reducing the air flow would not, for that reason, result in better gas exchange. More air flow would have the same total "contact", but would be more fresh at any given time.

What may be happening in your case is when the air flow is too high, the scrubber does not drop the CO2 as much as when the air flow is lower, so with higher air flow (good for exchange in the skimmer) you are actually using higher CO2 air (bad for raising pH).

In any case, I wasn't able to maintain 8.2 for a full week. Busted my bubble. Or, possibly, busted a whole bunch of tiny ones. My pH is back to 7.9 to 8.1.

I stopped fretting about it for now because I have this HUGE ORP problem.

 

[Randy Holmes-Farley]

In any case, I wasn't able to maintain 8.2 for a full week. Busted my bubble. Or, possibly, busted a whole bunch of tiny ones. My pH is back to 7.9 to 8.1.

I stopped fretting about it for now because I have this HUGE ORP problem.

lol

 

[Dkmoo]

Thanks for the input! I figured out what was wrong. The "recirculating" set up caused two issues - 1) the air was too moist that it formed a pool on the bottom of the canister that actually crusted the bottom layer of the media. 2) the hole from the skimmer lid back to the "in" was also too small causing not enough air to pump into the skimmers. I have since opened it up to use room air and it stabilized after a couple of days. Ph is now "stable" at 8.3 but already burned thru most of the media =/

I'm redesigning the recirculating set up by adding a moisture trap and changing the skimmer lid interface to see if i can make the recirculating work better.