Dropping pH

[meidenshink]

I've been fighting a dropping pH in my old 75 gallon and now am running into this in my newly set-up 125 g. Trying to narrow this down on my own, I've had my pH probe in a 5g bucket where I've been mixing my saltwater to add for water changes. I have this bucket airated to oxygenate and mix salt. My unmixed water shows around 8.2, and when I initially add salt it's about the same. A few hours later, there's a drop, and within 24 hours it's well below 8. So it doesn't appear to be something in the tank itself. My water? The salt brand? Could probe be inaccurate? Any ideas as to what's going on?

 

[btldreef]

Firstly, welcome to the site!
A few things:
What are your alkalinity and calcium readings?
How fast is the pH dropping exactly?
How much surface agitation do you have?
Run a skimmer?
What probe?
When was the last time you calibrated the probe?
Is the salt water in the bucket the same temperature as the saltwater in your tank?
Any corals in this tank?
Fish?
Inverts?
What is your lighting schedule?

 

[bang guy]

Quote:
Originally Posted by meidenshink http:///t/390711/dropping-ph#post_3461505
My unmixed water shows around 8.2, and when I initially add salt it's about the same.
Are you saying that your fresh water has a PH of 8.2? This is a possible issue.

 

[meidenshink]

I haven't measured Ca.
dKH 28
Good surface agitation in tank and bucket (bucket has aerator making plenty of bubbles).
I do have Marineland skimmer (it may be undersized for my new tank -- but used in 75g and no Nitrite/Nitrate issues when in use)
pH monitor is American Marine Pinpoint. I purchased new calibration solution and re-calibrated about 2 months ago.
I have Yellow Tang, Percula Clown, Blue Damsel, Blue Hippo Tang. Also three green mushrooms, emerald crab, peppermint shrimp, sand sifting star, and handful of hermits and snails. Shallow Aroganite fine sand bed and live rock. LED lighting 10 hrs/day.

 

[meidenshink]

Did some more measurements on this ... initial pH of RO water is at 8.5. Aerated for not even a minute and reading is down to 8.2. I'm vaguely remembering an article listing low Oxygen/higher CO2 in ambient air of some homes causing pH drop (might make sense here in MN during winter when we have the place as air-tight as posible to keep cold out?).

 

[bang guy]

Quote:
Originally Posted by meidenshink http:///t/390711/dropping-ph#post_3461570
Did some more measurements on this ... initial pH of RO water is at 8.5. Aerated for not even a minute and reading is down to 8.2. I'm vaguely remembering an article listing low Oxygen/higher CO2 in ambient air of some homes causing pH drop (might make sense here in MN during winter when we have the place as air-tight as posible to keep cold out?).
Interesting that it comes out of the RO at 8.5. I was only worried that it may be too high in carbonate but if it's RO water then that's not possible. No worries, ignore my concern. Your probe appears to be accurate if freshly mixed saltwater reads a PH of 8.2.
I wouldn't blame the salt or your water. You need to know the alkalinity.
It could very well be excess CO2 in the water. There may not be anything you can do about it but it's easy to test for. Just take a sample out of the house and see if the PH rises over an hour.

 

[flower]

Quote:
Originally Posted by meidenshink http:///t/390711/dropping-ph#post_3461568
I haven't measured Ca.
dKH 28
Good surface agitation in tank and bucket (bucket has aerator making plenty of bubbles).
I do have Marineland skimmer (it may be undersized for my new tank -- but used in 75g and no Nitrite/Nitrate issues when in use)
pH monitor is American Marine Pinpoint. I purchased new calibration solution and re-calibrated about 2 months ago.
I have Yellow Tang, Percula Clown, Blue Damsel, Blue Hippo Tang. Also three green mushrooms, emerald crab, peppermint shrimp, sand sifting star, and handful of hermits and snails. Shallow Aroganite fine sand bed and live rock. LED lighting 10 hrs/day.
dkh....28???? Shouln't it be somewhere between 7 to 11?

 

[bang guy]

28dKH, yeah, I didn't see that earlier. I'm not sure I've ever had a test kit that would even measure that level. Have you had that double-checked?

 

[meidenshink]

Only thing I can think of to offset high CO2 levels is stock the refugium I'm setting up with lots of Macroalgae ... do you think this would have an impact?
I'm glad you guys pointed out the dKH issue (I did double check and got same reading), that was my next question -- how concerned should I be with this, and what effects might I see because of it.

 

[bang guy]

28dKH is a serious problem. First thing is to verify the level using an alternative test. A different test kit, a local fish store, a fello hobbiest. Don't do anything until you get that second opinion.
If 28dKH is accurate then you need to mix up some new saltwater and test it to see if you have a bad batch of salt. If the salt is OK then begin a series of 10% water changes. I'd suggest every day do 10%. You do not want to alter Alkalinity all at once.
Alkalinity that high is going to cause the Carbonate in the water to combine with the Calcium. This could be what is lowering your PH if that truly is an accurate Alkalinity reading.
The idea of macroalgae in the refugium removing CO2 is valid. It does work and it works very well. Keep the light on 24/7 though as macroalgae stops consuming CO2 in the dark and actually produces CO2. Once things are under control you can light the refugium 24/7 or to save energy, light it opposite the display tank lighting.

 

[meidenshink]

Thanks, everyone, for sharing your time and expertise!
I haven't yet double checked dKH from alternate test, but my newly-mixed water tests at 12. I've started water canges.
Hopefully I can get fuge set up soon and get good ammount of macroalgae ordered.

 

[bang guy]

Quote:
Originally Posted by meidenshink http:///t/390711/dropping-ph#post_3462579
I haven't yet double checked dKH from alternate test, but my newly-mixed water tests at 12.
This gives me confidence in the accuracy of your test kit.