RO/DI water plus Red Sea Salt = 7.1 pH?

[whybenormal]

When you start out is the RO/DI Water Cold? I found out with Reef Crystals, and Cold Water, I don’t get a good mix, by dumping all the Salt in at once. I go with half the Salt, add the Heater. After the Salt is completely dissolve, and water is clear. I dose 1/4 the Salt, then slowly bring it up to 34.5ppt. BTW, initially I use a Danner 2 pump, in a 30 or 40 Gallon Brute.

With Red Sea you are supposed to have the water less than 68. I found with my 5 gallon bucket it was totally mixed in 30 mins just with running a powerhead. I'm just switching over from Reef Crystals - I had a much harder time mixing that.

 

[whybenormal]

**Update on my tank**
After a water change using water from the LFS and Red Sea of about 10 gallons, today my tank is showing 8.0-8.1 ph.

**Update on water testing**
I reran all tests today and a few more.
I ran a few gallons of RO/DI water, and am fairly certain I need new filters, as the TDS read 17.

To be certain my handheld pH meter was working I tested it with the calibration solutions and borax. Everything tested well.

My RO/DI water tested 5.4 pH @ 57.6 degrees, the meter is supposed to correct for temp, but I'm including it just because.
The Alkalinity read 1.9 (?) My test kit you count the drops and it only took 2 drops, so...

I mixed up a liter of saltwater, using the prescribed 38.2 g of salt (I measured it with my gram scale) and mixed it with my magnetic stirrer until dissolved.
pH read 6.4
Salinity read 1.026

I took 16oz and put an airstone with outside line for 60 minutes,
the rest I left on the magnetic stirrer for 60 minutes

The airstone water - reached 8.0 after about 20 minutes, and at 60 minutes was still at 8.0.
Alkalinity was 10.47
The water on the magnetic stirrer reached 7.8 just on my kitchen counter.

The pic is just my "mad scientist setup" bc my husband thinks it is funny.

 

[MarineandReef Jaron]

Great to see how this progressed. It looks like CO2 is the culprit.

 

[thatmanMIKEson]

**Update on my tank**
After a water change of about 10 gallons, today my tank is showing 8.0-8.1 ph.

**Update on water testing**
I reran all tests today and a few more.
I ran a few gallons of RO/DI water, and am fairly certain I need new filters, as the TDS read 17.

To be certain my handheld pH meter was working I tested it with the calibration solutions and borax. Everything tested well.

My RO/DI water tested 5.4 pH @ 57.6 degrees, the meter is supposed to correct for temp, but I'm including it just because.
The Alkalinity read 1.9 (?) My test kit you count the drops and it only took 2 drops, so...

I mixed up a liter of saltwater, using the prescribed 38.2 g of salt (I measured it with my gram scale) and mixed it with my magnetic stirrer until dissolved.
pH read 6.4
Salinity read 1.026

I took 16oz and put an airstone with outside line for 60 minutes,
the rest I left on the magnetic stirrer for 60 minutes

The airstone water - reached 8.0 after about 20 minutes, and at 60 minutes was still at 8.0.
Alkalinity was 10.47
The water on the magnetic stirrer reached 7.8 just on my kitchen counter.

The pic is just my "mad scientist setup" bc my husband thinks it is funny.

Me too

 

[arking_mark]

**Update on my tank**
After a water change using water from the LFS and Red Sea of about 10 gallons, today my tank is showing 8.0-8.1 ph.

**Update on water testing**
I reran all tests today and a few more.
I ran a few gallons of RO/DI water, and am fairly certain I need new filters, as the TDS read 17.

To be certain my handheld pH meter was working I tested it with the calibration solutions and borax. Everything tested well.

My RO/DI water tested 5.4 pH @ 57.6 degrees, the meter is supposed to correct for temp, but I'm including it just because.
The Alkalinity read 1.9 (?) My test kit you count the drops and it only took 2 drops, so...

I mixed up a liter of saltwater, using the prescribed 38.2 g of salt (I measured it with my gram scale) and mixed it with my magnetic stirrer until dissolved.
pH read 6.4
Salinity read 1.026

I took 16oz and put an airstone with outside line for 60 minutes,
the rest I left on the magnetic stirrer for 60 minutes

The airstone water - reached 8.0 after about 20 minutes, and at 60 minutes was still at 8.0.
Alkalinity was 10.47
The water on the magnetic stirrer reached 7.8 just on my kitchen counter.

The pic is just my "mad scientist setup" bc my husband thinks it is funny.

So your pH meter is definitely off by about 0.37 if you trust your alkalinity measurement for the outdoor aerated seawater.

So no mystery here. pH measurements are inaccurate and your seawater is fine with proper aeration.

If you believe your indoor pH measurement of 7.8 for aerated seawater, then your indoor CO2 is 1800ppm.

At this level, it's unhealthy for humans and you would experience health issues with extended exposure...you would notice this.

 

[Randy Holmes-Farley]

I agree it sounds like CO2 is getting through the depleted di.

 

[Jeeperz]

This is why spectrapure had me run my RO water to a brute with a big air stone, after 24 hours I pump it through the DI at a rate of ~12-16 ounces a minute. I've made well over 2500 gallons of 0 tds water after the DI doing this. I have high co2 in the city water(comes from a huge well field in north Idaho) My incoming tdsis around 90 if I remember right and after the 99% spectrapure membranes I get 0 tds, and zero tds between both di stages and after.

I've made a minimum of 40 gallons rodi per week for over 2 years now on the same filters

 

[Randy Holmes-Farley]

With Red Sea you are supposed to have the water less than 68. I found with my 5 gallon bucket it was totally mixed in 30 mins just with running a powerhead. I'm just switching over from Reef Crystals - I had a much harder time mixing that.

Lower temperatures decrease the likelihood of precipitating calcium carbonate as the salt mix dissolves, but there is no magic temp that is OK and not OK.

 

[biom]

My RO/DI water tested 5.4 pH @ 57.6 degrees

Wow, you can run a calcium reactor with this pH, actually it is too low for calcium reactor which requires about pH 6.5. Honestly I don't believe US authorities will allow tap water with pH 5.4 to run in public infrastructure, because of health regulations, not speaking what this highly acidic solution will do with metal pipes. So It looks it is your DI resins doing something very wrong.
Very nice "mad scientist setup" you have by the way

 

[Randy Holmes-Farley]

Wow, you can run a calcium reactor with this pH, actually it is too low for calcium reactor which requires about pH 6.5. Honestly I don't believe US authorities will allow tap water with pH 5.4 to run in public infrastructure, because of health regulations, not speaking what this highly acidic solution will do with metal pipes. So It looks it is your DI resins doing something very wrong.
Very nice "mad scientist setup" you have by the way

pH of RO/DI is a suspect measurement, at least when it is zero ppm TDS, but it is expected that totally pure fresh water in contact with indoor air will have a pH in the 5's.

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Final Effluent pH

Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).