RO/DI water PH levels???

[anaya]

My RO/DI system consistently produces water with 0 TDS but a PH level consistently at 7.8, I do a complete filter set replacement every 6-8 months and/or when the TDS reads above 0. Is this normal for a system to produce?

Is it necessary for me to continue spending $7.00 a week on buffer to bring the PH up to 8.3? Or could there be something else I can do to fix the PH issue?

Thank you for any input.
Antonio

 

[anaya]

After researching and putting more thought into this issue I believe I may have found the main issue. The containers my RO/DI system fill (both a salt and fresh water) are completely air tight which does not allow for the proper gas exchange allowing the pH to be maintained at an acceptable level (although 7.8-8.5 is the known acceptable level I am aiming to keep it around the natural pH of sea water which is 8.2 if I'm not mistaken).

My first attempt to solve the issue will be adding a luft pump and air stones to my storage containers in hopes to lower CO2 levels and raise the O2. My setup is in an exterior laundry room from the house with a ventilation fan on one side and a screen door on the other. It should work as long as I keep the fan running to be sure there is proper ventilation. I will drill holes in the containers to feed the airline through and another to let the forced air out and mount the luft pump as close to the screen door as possible without being so close that it gets wet from rain.

If there are any possibilities I missed please chime in to point them out.

Antonio

 

[reefgeezer]

IMO... as long as the RO/DI unit is functioning properly, there is no need to worry about pH or spend money trying to change it. In addition, adding buffer will raise alkalinity more than it will change the pH and is the wrong way to approach the problem. If your system is performing properly, the initial pH of the water could be higher than it is after the gases (CO2) stabilize. However, stabilization will also happen when the water is mixed with salt mix or when it is added to the tank as top off.

 

[disc1]

The RODI water has ZERO buffering capacity. That means that chemically, its pH doesn't mean squat. The pH of your top off water will have absolutely zero effect on the pH in your tank. You should never buffer your top off water unless your intention is to buffer the tank and you are simply using the ATO as a means to deliver it. Otherwise, the water in your ATO should be pure pure water and you don't need to add anything to it.

 

[anaya]

reefgeezer and disk1: My apologizes, I was not being clear on my second post and left out some details. The water coming directly out of the RODI and after mixing with reef crystals salt is at 8.4. I had realized I was only testing the water in my holding containers and then proceeded to test the water coming out of unit freshly mixed instead. Which indeed narrowed the issue to the holding containers and not my unit.

reefgeezer: Thank you for pointing out how the buffer raises the alk, I had no idea it had that effect. I had never added buffer to the top off water just the tank after weekly water changes other wise the pH would sit at 7.8.

So should I only try the airstone in the premixed salt water holding container? Or is this method completely pointless?

 

[disc1]

Sorry I misunderstood. I thought you were talking about the pH of the RODI water. Yes, it is a good idea to mix and aerate your salt water for a couple of hours before you do your water change. There's no need to worry about it until right before you use it though.

And yes, all pH buffers raise alk. There is no possible thing you can add that would raise pH and not alk, it's just a chemical impossibility. In most every case, the same air/CO2 issue is responsible for low pH in the tank.

 

[disc1]

I had realized I was only testing the water in my holding containers and then proceeded to test the water coming out of unit freshly mixed instead. Which indeed narrowed the issue to the holding containers and not my unit.

And just FTR, your RODI unit has absolutely no effect on the pH of your mixed salt water ever. It just doesn't. Nothing that the RODI does or doesn't do, and nothing about the pH of the water that comes out of it has any bearing on the pH of the water afterwards. That's all a product of the salt mix and the CO2 in the air that dissolves into the water.

 

[anaya]

disk1: thank you for clearing that up for me. My tanks are all eel tanks with solid glass lids (3/8" holes drilled in a 4" grid pattern), sumps, closed loop and skimmers. So is it plausible the lids are contributing to the issue? I suppose there could be a CO2 buildup issue in my house in general. I will try to open the windows at night for a bit while it's still cool enough outside.

 

[bertoni]

The lids might be reducing the air flow enough to make a difference. I guess you could try forcing air into the system for a bit with an air pump or the like, or maybe take it off for a few hours when you can be around. Outgassing carbon dioxide can be a slow process, which is why I say three hours or so. It sounds like leaving the house windows open is an easier experiment.

On the other hand, a skimmer can do a lot of aeration, and it's possible that the glass isn't making a difference.

 

[FragIt Dan]

Take a gallon of your tank water and sit it in an open container beside your tank. Measure the pH of both your tank and the removed water upon removal and again several hours later. If the pH differs significantly then I would suggest aeration is limited and may be the driving factor pushing your pH down, depending upon how big the difference is. Personally, I would have thought your skimmer(s) and air holes would be providing enough gas exchange, but perhaps not. Keep in mind respiration occurring in the tank (but not in your water sample) will account for about 0.2ish pH difference. If your removed water sample returns to appropriate pH you should be able to assume aeration is your issue. Just an idea...

 

[anaya]

FragIt Dan: I will try that now, thank you. I also figured with the skimmers and drilled lids that this would not become an issue. I am honestly beginning to think there may be a fresh air issue inside the house. If what you mentioned trying and what I'll try tomorrow with the lids fails to work I will attempt to leave a window on the opposite end of the house from my AC intake open for a few days to get fresh air coming in constantly.

bertoni: I'm off all day tomorrow so I believe I will try to remove lids and open windows in the house. I had thought about putting the luft pump outside and running air lines to each tank but if I can avoid that it would save me lots of frustration from trying to work in the 18" crawl space under the house where I would need to run the air lines.

 

[FragIt Dan]

FragIt Dan: I will try that now, thank you. I also figured with the skimmers and drilled lids that this would not become an issue. I am honestly beginning to think there may be a fresh air issue inside the house. If what you mentioned trying and what I'll try tomorrow with the lids fails to work I will attempt to leave a window on the opposite end of the house from my AC intake open for a few days to get fresh air coming in constantly.

I have actually just returned from a conference in Seattle that in part dealt with Ocean Acidification with respect to excess CO2. Data presented showed city air pollution can and does have localized acidifying effect on Ocean pH via excess CO2 with some reported ecoregions measuring CO2 levels in excess of 1000ppm (compared to 300-400ppm ambient levels). I think it would be fairly safe to assume those of us living in areas where the ocean would be affected would see effects on pH in our tanks during times of excess CO2, but again, the source is outdoor air and so opening windows will not solve this.
Counter to this, Robert Jordan wrote a great article in Advanced Aquarist:
http://www.advancedaquarist.com/2002/4/short
that shows CO2 build up at night can push pH down by amounts you are reporting. I think if you were to add nightly affects and outdoor pollution together it could easily explain what you are observing. Opening your windows may mediate some of the issues, but if you live in a metropolis, it may not alleviate them all.
Dan

 

[anaya]

FragIt Dan: I will read that article after typing this, Thank you. I have tried all the suggestions and the ideas of my own. Leaving the windows open the last few days has the tanks testing at 8.0 (with API and Instant Ocean kits). I will also be ordering a pH test probe hoping to eliminate as much human error as possible. I'm left with the thought of not doing the monthly macro trimming in the tank in hopes to raise the O2 levels... but at this point I am not even sure that CO2 buildup is the issue causing the low pH. I'm baffled... I suppose I will be loosing my head in books and all the articles I can find this weekend to uncover all the possible causes.

 

[Randy Holmes-Farley]

FragIt Dan: I will read that article after typing this, Thank you. I have tried all the suggestions and the ideas of my own. Leaving the windows open the last few days has the tanks testing at 8.0 (with API and Instant Ocean kits). I will also be ordering a pH test probe hoping to eliminate as much human error as possible. I'm left with the thought of not doing the monthly macro trimming in the tank in hopes to raise the O2 levels... but at this point I am not even sure that CO2 buildup is the issue causing the low pH. .

There is NEVER, EVER any explanation for low pH than excess CO2, assuming alkalinity is normal or high. pH, CO2, and alkalinity are exactly related mathematically in seawater, and if you know two of them, you can determmine the third exactly.

FWIW, O2 has nothing to do with pH.

pH 8.0 is fine. If you want it higher, the best solutions are lower CO2 air (fresher air or a CO2 scrubber) or adding a high pH alkalinity additive (best is limewater, second is carbonate alk additives). Another option is using up CO2 with photosynthesis.

There are no other options.