Battling CO2 in Source Water

[Tihshho]

Since I've seen one person dealing with this and countering it on their DI unit, I figured I'd put up a topic about this. Anyone else have an issue with saturated CO2 in their source (tap) water? I've generally had to be careful about huge water changes in tanks that didn't have plants or multiple points of aeration, because otherwise I'd gas out the fish. Does anyone supplement peroxide in their tanks when filling to counter this?

[Zenzo]

On 9/12/2021 at 11:23 AM, Tihshho said:

Since I've seen one person dealing with this and countering it on their DI unit, I figured I'd put up a topic about this. Anyone else have an issue with saturated CO2 in their source (tap) water? I've generally had to be careful about huge water changes in tanks that didn't have plants or multiple points of aeration, because otherwise I'd gas out the fish. Does anyone supplement peroxide in their tanks when filling to counter this?

Interesting. Are you measuring o2 levels when refilling the tank? This is nothing that I have ever encountered. What about having a lot of surface agitation and a little bit cooler temp water when doing water changes? Cooler water tends to hold more o2. I have the nozzle of my refill hose blasting at the surface in some of my larger tanks. 

[gardenman]

From an aquarist's perspective, keeping CO2 in the water is harder than getting rid of it. It off gasses pretty readily. I would assume that just storing it for a few hours before using it would let most of the excess CO2 off gas and the water would be good to go. Some aeration would speed the process up even more. Storing water for later use with some plants in the holding container could speed things up even more. As water issues go, too much CO2 is one of the easier ones to deal with.

[Tihshho]

On 9/12/2021 at 11:44 PM, Zenzo said:

Interesting. Are you measuring o2 levels when refilling the tank? This is nothing that I have ever encountered. What about having a lot of surface agitation and a little bit cooler temp water when doing water changes? Cooler water tends to hold more o2. I have the nozzle of my refill hose blasting at the surface in some of my larger tanks. 

This isn't a topic that gets discussed a lot on the freshwater side. Most people notice it one of two ways, water tests being done when purchasing a home (on a well) checking that it's potable as well as what's in it or the most common is for the reef folk running RO/DI units seeing that their mixed bed resin isn't being effective long term or if they have a split bed the anion or cation (can't remember which) gets exhausted quickly (within say 120 gallons of product being formed.) Since the water is coming from a deep well (~550 feet) I'm not sure there is enough gas exchange to keep up with O2 saturation, there's probably more to it but I've not looked that much into the cause. Chemically, if you test water directly out of the tap for pH, depending on the season and temps, you can get a pH of 5.5-6.5 and if you test a bucket of aerated water after a few hours you'll get a pH of 7.5. I've also noticed in planted display tanks and had the water fill flowing past the CO2 drop checker before the CO2 kicked on, depending on how much water was being changed, the reagent would turn yellow or be a light green without even having the CO2 on. This is a major reason why I always recommend folk to test pH of their water after letting it sit overnight since the values you see upfront could be drastically different from the tap to an agitated container/tank that has no buffer added. 

Cool water would make sense, but I run a dedicated cold line to my RO/DI system and this is the baseline I'm using for the CO2 saturation as I'm lucky to get 120 gallons of product water without having to replace a full stage of contents. The other signs are that with heavy heavy water changes fish go from happy to gasping at the surface or in the case of some shrimp are instantly gassed out. 

I have a python hook that I've modified so that the water hits a surface to agitate it and then directs the water out the sides rather than directly down. I also use a clamp to hold the outlet as high as I can in tanks so that the in coming water has to splash into the tank to agitate it even more. This process works the best so far, but I'd still like to find another way of adding O2 besides splashing the water going in, relying on the air from sponge filters and an additional air stone bar during water changes.  

On 9/13/2021 at 9:34 AM, gardenman said:

From an aquarist's perspective, keeping CO2 in the water is harder than getting rid of it. It off gasses pretty readily. I would assume that just storing it for a few hours before using it would let most of the excess CO2 off gas and the water would be good to go. Some aeration would speed the process up even more. Storing water for later use with some plants in the holding container could speed things up even more. As water issues go, too much CO2 is one of the easier ones to deal with.

This is definitely something to consider with limited tanks. In my case, I change hundreds of gallons of water a week it's not exactly feasible unless I split water changes up to two tanks get done per day and I do water changes almost daily to split up the load. I have a process now that 'works' to not gas out the fish, but I would like to find a process that I can use to get more O2 upfront especially so that I can simulate the rainy season for some species like I used to at my old place. 

[Bullsnark]

I know this isn’t what you’re asking, but what about getting yourself a holding tank and stock it with hornwort or something. Use that tank as you source for water changes, then top it off afterwards. Something like a rain barrel for catching downspout water would be ideal. 

[Tihshho]

On 9/13/2021 at 10:42 AM, Bullsnark said:

I know this isn’t what you’re asking, but what about getting yourself a holding tank and stock it with hornwort or something. Use that tank as you source for water changes, then top it off afterwards. Something like a rain barrel for catching downspout water would be ideal. 

Issue is that the holding tank would have to be able to store over 100 gallons of water and then the space related to storing said vat. I'd rather not be using a vat with plants since that would mean I'd have to light it and fertilize it in between water changes.