Aging saltwater

melev

melev

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When I mix up 55g of saltwater in a barrel, I fill it up with RO/DI first. Then I add the salt, a Rio pump and a heater and let it mix for a day.

What I'm discovering is when I leave it mixing for a few days, pH really drops substantially. Rick, have you ever checked your saltwater's pH that you age for 14 days? I'm wondering if I add a venturi to the pump to draw in air, it should help raise pH perhaps. The water is circulating, but very quietly and smoothly. The surface moves, but doesn't ripple.

I'm just curious if anyone else has seen the same thing with their saltwater after letting it mix for a few days before using it.
 
the longer I let mine sit the clearer it gets so I figured that it takes quite a while for eveything to dissolve. Filled a old tank with 20 gals. RO and added salt waited 24 hrs, PH was about 8.2. About 4 days later it was 7.7. So I store it in a closet for about a week circulating and PH stays stable @ 8.3.
 
So why does it drop to 7.7 then later go back up to 8.3? I saw mine hit 7.5 or maybe lower, and used baked Baking Soda to boost the pH back up to something near my tank's current level.
 
I let it mix for three weeks sometimes. But I aerate it . I have the hose hooked up to a mag pump that I use to mix and pump the water into my tank. I hung a bungie cord across the top, take the end of the hose suspend it above the water surface. Then the pump is on a timer, comes on a few hours a few times a day. And as it mixes, it drops the water down from the surface through the bottom where the pump is. It has been working okay for 4 years.
 
My last batch has been mixing for a week and is currently at 8.1. I use a 620 gph CAP pump with a venturi attached, running 24x7. I like the timer idea, think I might give that a try. :D
 
I think aeration, or the lack thereof, is my problem. Thanks for the feedback.
 
Marc I would be curious for you to do a bit of an experiment. If you have the room and equipment available, set up two pales at once, mix up the salt, for the control continue to do what you are doing, while aerating the experiment pale. I would be curious to see your parameters with everything equal. Would be cool to post on your web site.

I'm not sure why the lack of O2 would cause a drop in pH? I don't think it acts as a catalyst, and if it did, I would expect the H20 and NaCl to buffer each other. I could see if there was an accumation of HCl from the dissociation of NaCl. My chemistry has all but since been forgotten!
 
@Marc wrote:
I think aeration said:
I agree.

@Servo wrote:
I'm not sure why the lack of O2 would cause a drop in pH? said:
The lack of O2 is not the problem but the increase of CO2 that decreases the pH. CO2 mixes more readily with water than O2 so without active aeration the O2 excapes into the room air and is replaced by CO2 that is in the air. Also there may be a certain amount (though not enough to overtly polute the water) of bacterial or algal respiration in the container that uses the oxygen and excretes CO2.
Click to expand...
Click to expand...
 
Yeah, I should do that, but I think I already know the answer, like Ryan pointed out.
 
Just an update. Yesterday, I tested the pH of the barrel of water, and it was 7.3 so I did as Rick recommended and had the hose pouring down onto the surface of the water. Three hours later, the number hadn't changed. So I added Seachem's 8.3 buffer, and brought the pH up to 8.5 in no time.

A day later, with the pump still breaking up the surface, the pH was 8.01
 
Okay, I just mixed up a new barrel of saltwater.

55g - RO/DI with a TDS of 1
Salt - Kent's Sea Salt
Current temperature - 70F and heating up
Salinity - 1.025 using a refractometer
pH - 6.55 (calibrated pH Pipoint Meter) after mixing for a few hours with two pumps, surface agitated well.

I'm starting to wonder if the batch of salt I got is bad/old. This was part of the group buy from Custom Aquatics we did a couple of months ago, and the artwork on the bucket was extremely old and does not even look like the buckets we get at the LFS.

I'll see what the pH is in the morning, but that seems exceedingly low.
 
Marc wrote:
pH - 6.55 (calibrated pH Pipoint Meter) after mixing for a few hours with two pumps, surface agitated well.

Quote:


:shock:

It "burns, it burns" said the little copepod. Actually, it think that it was your salt water that Dorthy threw on the wicked witch of the west!


 
I think I figured out the problem with the pH - I did a test with a multimeter, and there is stray voltage in the mixing barrel. When I take a cup of water out of the barrel and test the pH, it is more like 7.65

Still low, but not nearly as rediculous as that previous reading.

Still, back to the older buckets of salt (based on the artwork of the bucket) - I've never bought Kent Sea Salt before to find it bagged inside the bucket. Normally I pop open the lid and see salt, but this bucket had a sealed bag inside. Strange.
 
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