pH drops as water sits out?

[Jonathan G.]

i have noticed that when i test my tap water out of the faucet it is perfect at 8.3 but after i have it sitting out and getting ready for a water change it drops to unbelievable amounts, like 7.7-7.8. i dont know what would cause this nor i dont know if it is enough to throw my whole tank off cause i only change about 5% every week. it boggles my mind how the pH drops so dramatically.... anyone have any ideas? I dont use ro/di water but where im at our tap water is pretty pure.

 

[Boomer]

The drop is due to ambient CO2 in the air. That CO2 can not get into the water lines but as soon as it is exposed to air the air mixes with the water and the pH falls. If you took that 8.3 water and blew in it with a straw you will see the same effect. You can raise the pH back up by adding a little kalk. The kalk will react with the CO2 and remove it. Any change in CO2 will change the pH.


In short
Ca(OH)2 + CO2 ----> Ca ( free calcium )+ HCO3( think baking soda)

 

[Al G.]

Sorry to piggyback on this thread, but would the ph drop on saltwater if left out?

I mix RO water and Oceanic salt in a covered Rubber maid trash can with a powerhead to a specific gravity of 1.025. When not used right away, the ph drops to a low 7.4 If I continously aerate it I can get the ph up to maybe 7.8, but unaerated it drops back to 7.4 The ph was tested with 3 different tests and they all gave similar results.

Am I mixing the sw wrong, or is this a bad bucket of Oceanic?

I've been adding Seachem buffer to get the ph up, before using the water for water changes.

 

[Boomer]

It may be something wrong with that Oceanic. Almost all salts have a high pH initially after it is mixed. Once it equilibrates with air, then it drops to around 8.1-8.3. Then again it may be high room air CO2.


I forgot to post these yesterday

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

Indoor CO2 Problems
http://www.advancedaquarist.com/issues/apr2002/short.htm

 

[Al G.]

Thanks for the reply and the cool links.

I made up a new batch of water with a new bucket of Kent salt. The pH was around 8.3 compared to 7.4 that I would get with the Oceanic salt. Bad bucket.
If anybody wants some Oceanic salt to test for other abnomalies, I got a lot left.

 

[Jonathan G.]

what if i use say my spare CA-2200 and hook up the air diffuser would this help oxygenate the water better? i also have a penguin 330 would this work better? im planning on switching to ro/di water as soon as i can save up some money. just bought my lights though so im kinda low on money. but my lfs is right near me and uses straight faucet water and has never had a problem with it. he has been in business for over 15 years but he said when he had his shop in chicago he used ro/di water cause the water quality there was much lower then here in ohio.

 

[Jonathan G.]

bad bucket of oceanic? are u serious, i thought that it was a good brand of salt. that really really really stinks. so i checked around and no place around here sells tropic marine or kent but i can get all the IO and reef crystals i want. should i try changing my salt or just get another bucket of oceanic? could i change my salt by keeping up my water changes at 10g a week for a 75g tank?

 

[Jonathan G.]

l also did a quick check and set out just a bucket of tap water and the pH comes out at 8.3 or higher but after it sits out for a day it drops down into the 7's

 

[Al G.]

Jonathan,
Search for Oceanic salt on Reefcentral, and you'll find a lot of long threads about bad batches of Oceanic.
I wasn't checking my pH regulary, until Flugelnuss on this board, tested all my tanks(3) and my saltwater storage container and found that they all had a pH of 7.4. All 3 tanks have skimmers on them, and only one of them is well stocked.
The article about high CO2 in homes was interesting and could possibly account for the exact same pH in all my tanks, but I made a new batch of sw with Kent salt, and so far the pH is staying up there.
I can't say for sure how bad a bucket of Oceanic salt I have, but it does look like it has a bad buffering ability. If it's just the buffer, I can easily use some Seachem/Kent/etc marine buffer, but I just don't know. I don't have the test kits or equipment to test out the other things that might be bad with this bucket of Oceanic.
Aside from the pH thing with this bucket(my 2nd bucket of Oceanic), I had no quarrels with Oceanic Salt, unlike the people on RC. Oceanic salt is being blamed for a whole lot things on that board. I'm going back to Kent salt, which I originally started the tanks with, just to be on the safe side.

 

[Jonathan G.]

k thanks for the advice... if i dont have tropic marine or kent around here should i just switch to I.O. or reef crystals?

 

[Al G.]

IO seems to be the salt of choice for alot of people. I just use Kent salt, because I can get it cheaper. From what I've read on RC, Kent buys there salt from the makers of IO, and then they boost some of the attributes. How true is that? I don't know.