Question about mixing Saltwater

[bripen]

I know that when using RO water you should aerate your mix 24 hrs. However, I use well water, and I am wondering what the mix time should be for a small amount of replacement water..i.e 3-5 gals?

 

[Boomer]

It makes no difference all should be aerated.

 

[bripen]

Why???? Not to argue--just want to understand--I thought the aeration was to restore lost oxygen, etc. from the RO/DI processing. Is this wrong? What purpose does mixing make-up well water for 24 hours versus 4 hours accomplish?

 

[shallowreef]

I've never aerated my water and i know a lot fish stores don't do this either. I don't think its all that important but more of a personal preference. I could be wrong but i have been doing reefs for awhile and have never practiced this method.

 

[Boomer]

O2 does not leave an RO/DI unit but CO2 does usually. Most gases go right through the membrane.

You want to make sure all the salt components are dissolved and to equilibrate the water's CO2 and O2 with the ambient air CO2 and O2. You can actually do all this in 5 min if you do it right.

How to Mix a Batch of Synthetic Seawater in Under Five Minutes
http://web.archive.org/web/20011217234403/www.animalnetwork.com/fish2/aqfm/1997/sep/bio/default.asp

 

[bripen]

Thanks, Boomer!

 

[shallowreef]

Not a bad idea.

 

[dnjan]

O2 does not leave an RO/DI unit but CO2 does usually.

Hey Boomer - could you clarify? Do you mean that disolved CO2 does not usually make it through the RO membrane?

Just curious.

 

[Boomer]

Your welcome

 

[Boomer]

No Don CO2 goes right through the RO membrane just like O2. CO2 is taken out by the DI. CO2 on the discharge of the RO mixes with H2O

2CO2 + H20==> H2CO3 ==> H+ + HCO3- ==> 2 H+ CO3--

The DI then removes the HCO3- and CO3--. This is why well water often depletes a DI rather quickly and why it is nice to know the pH and Alk of the input line water. Well water is often hgih in CO2.

Lets pretend the pH is 6.5 and the Alk is 4dKH on the "tap-water" line . And the RO output TDS is 10 ppm

CO2 = ^&**&^^% X $#@% / *&%$ (I'll give you the real equation if you want it )

But for FW this works great.
http://jerbaker.dhs.org/fish/calculators.html

CO2 = 38 ppm


So, 38 + 10 = 48 and 38 /48 = .79 or 79 % of the DI resin will be taken up/depleted/exhausted souly buy CO2.

 

[dnjan]

Thanks. I was just curious about what was taking out the CO2.