Fun with water pH

[Yoimbrian]

so I'm confused by my pH and I'm hoping someone can help me figure it out. I'm not even talking aquarium pH either - just water.

So here's my situation:
-well water
-out of well has high iron, calcium, and hydrogen sulfide
-whole house water softener (gets to zero iron and 0 hardness)
-whole house carbon filter (removed hydrogen sulfide)
-RO system for drinking water, which also has a "remineralization" cartridge. Top of the line for all of the above 3, Kinetico brand.

The tap water comes out at ~7.4, and then over 12 hours drifts up to ~8.4.

The RO water comes out at ~8.2 and then drifts down to ~7.4.

why does the tap water go up? My only theory is hydrogen sulfide is still there and slowly off gases. But then why does the RO start so basic? I figure that comes down because of CO2?

Also. RO for the aquarium is not an option. My septic tank is 60 years old and I'm already worried about a 180 gallon aquarium. Using 5x the water (due to RO waste) would flood it for sure.

 

[tarheel96]

What's the TDS of the water remineralized? This is the water that settles at pH 8.4? Or is that just the well water?

CO2 lowers pH. Your tap water that rises to 8.4 does so because it contains CO2 from the well. I'm not completely sure about the RO water which drops in pH except that this is usually due to a vacuum of CO2 relative to water at atmospheric pressures.

Water plants add sodium hydroxide which removes CO2 and raises pH until the water exits the tap and vents with the atmosphere. As CO2 then enters the water, the (sodium) hydroxide is broken down and pH falls to its natural level. This is not what's happening in your case but it's an example of a CO2 vacuum elevating pH.

 

[Yoimbrian]

That is the water report from our un filtered well water. So after the water softener that calcium will be sodium. The rest of the report is just a bunch of random organics that we tested negative for.

 

[tarheel96]

Based on on alkalinity of 260 mg/L (as CaCO3) a high pH over 8 should be expected. 260 / 18.65 = 14dKH which is very alkaline. Once the water exits the tap, it takes about 12-24 hours for the excess CO2 to gas out during which time pH gradually rises.

Total dissolved solids should rise a little as sodium replaces calcium and magnesium because Ca and Mg both +2 and sodium is only +1 but that's not a problem.

http://www.endmemo.com/chem/cationanion.php

I think you mentioned you were planning on using well water for your tanks. I think that is best anyway. I'd use this well water harder water fish before using the water from the water softener. This includes a lot of fish but especially those from African rift lakes and Central American. Even fish from other locations considered soft water can work.

 

[duanes]

I agree with Tarheel96, I'd use straight well water, before softening for the fish.
And also agree it it could be the CO2 lowering the pH temporarily.
And if I were the yoimbrian, I'd tailor the species I keep, to the highly mineralized well water, not the opposite of trying to alter the water.
And with the high iron content, I'd heavily plant my tanks (or attach heavily planted refugiums, if the fish are plant destroyers) with plant species that use Fe.

 

[Yoimbrian]

Interesting. Thanks for the info!

Not sure I can bypass the water softener without also bypassing the sediment filter and carbon filter, but I'll look in to it

 

[deeda]

Usually the water softener has bypass valve installed but it will vary depending on the installer and the system requirements.

Pics of the equipment setup from well main line to final treated water output may be helpful.

I have the old Kinetico Model 60 dual tank softener and it has the integral bypass valve that I switch when I do water changes for my tanks. Just a whole house sediment filter prior to the Kinetico and also have a tank-less water heater so don't have to worry about mixed softened and hard well water.