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euromomtx
10/12/2009, 11:07 AM
I've been making my saltwater from purified (RO) water in a 10 gallon trash can with 1 water pump for circulation and 1 heater.

Up until now I have been using Oceanic salt and it did have a lot of precipitation so I just bought some Reef Crystals.

My pH was hovering around 8.0 in my display tank and low in alkalinity so I added over the course of some days some baking soda. That brought up alkalinity and pH to 8.4.

Then I did a water change and pH dropped down to 7.6 (from just a 10% water change!)

How can that be? Isn't new water supposed to keep pH stable or even raise it?

I had used up most of the Oceanic by that time so refilled with a batch of Reef Crystal water (still had some Oceanic water and all of the precipitation left in the trash can though).

I probably should have completely cleaned out the container before making a new batch.

This time I remembered to check the ph of the freshly amde water though and it is 7.5 pH.
I don't understand why my freshly made seawater from two different brands ends up being so low in pH. What's going on?

At this point the alkalinity in the display tank is at appropriate levels so I am hesitant to add any more baking soda.

tmz
10/12/2009, 11:16 AM
What sg is your newly made water?
How are you testing ph?

euromomtx
10/12/2009, 11:23 AM
salinity is 35 ppt (sybon refractometer)
I tested the pH with strips, Seachem Test Kit and mostly with my pinpoint pH meter.
I calibrated the pinpoint meter last night and it seems to be accurate. Pinpoint says 7.67 in DT and 7.48 in new saltwater.

Edited to add: my regular test is from red sea and seems to be in line with what pinpoint says.
We make the RO water at home.
I just made a small batch of saltwater and tested it and it was 7.6 pH.

Maybe it's my RO water? Can tap water be acidic?

bertoni
10/12/2009, 05:49 PM
Tapwater is unlikely to be acidic. The chemicals added to it make it basic. What was the alkalinity of the saltwater batch that tested at 7.6, and how long was it aerated after mixing? I'd try aerating a cup of that water outside for a few hours, and then measure the pH again.

euromomtx
10/12/2009, 06:55 PM
The alkilinity of the one testing 7.6 was over 3.6 meq/l!
After aerating it for a couple of hours it rose to 8 pH!

bertoni
10/12/2009, 10:17 PM
Okay, that pH is fairly believable. The low pH is caused by a high carbon dioxide level in the water. Fresher air or more aeration, or both, might be needed to get the pH back to normal. If aerating some tank water inside the house raises the pH, the tank needs more aeration. If aerating the same sample outside the house is required to reach a good pH, the system needs fresher air from outside. Limewater as autotopoff can simulate fresher air to some degree, since it consumed carbon dioxide from the water column.

euromomtx
10/14/2009, 02:48 PM
Hanging the airline out the window and connect it to the skimmer has worked really well! My pH in the tank is back to acceptable levels.
I came across this gadget and was wondering what you guys thought of it:
http://www.mcuresearch.com/co2.html

bertoni
10/14/2009, 03:02 PM
There's been some speculation that some of the carbon scrubbing media might be very useful for aquariums. I can't tell from the description what kind of media this unit has, and how cost-effective it is, but the idea might work very well.