Shelf life of mixed saltwater

[nyc reefer]

I'm curious water if any is the shelf life of mixed saltwater? I have rebooted my 34ga tank and only plan on 5ga water changes a week if I mix a bag of reef crystals which makes 50ga and change 5ga a week technically I would have water for 10 water changes. Would I need to keep the pump on at all times or only before a WC to oxygenate the water?

 

[Boomer]

How long has it been mixed ?

 

[Chefjpaul]

Here's my take;
issue with this; you can over mix synthetic salt water and the chemicals can precipitate out: aka CA & MG carbonate, KH, PH can be almost non existent, just to start with.
With most salts being over mixed you'll also end up with a calcification / residue from.

I personally just have RODI water always ready, as most salts will mix in about an hour or so, and say to NOT over mix, you'll need to read about your particular brand, as an example, RSCP Mixes in about 45 min. Per 5G.

To keep it constantly mixing, can also cause evaporation and raise the salinity.

http://reefkeeping.com/issues/2005-07/rhf/#2

 

[Hefe-Weizen]

I have been mixing my salt by hand about an hour prior to the water change. I use a plastic stirrer and mix it until it's clear and fully dissolved. Heat it and do the water change. Never had any issues using IO or reef crystals.

 

[Chefjpaul]

You can mix salt and leave it covered. I do that, I think op was referring to keeping it mixing constantly.

 

[Boomer]

It should be mixing constantly to keep it in equilibrium with the air. And if it sits to long without circulation ions/ salts start to get more concentrated in various areas as function of ion to ion attraction, density and temp and layering of gases, aka, settling. To reduce any potential loss of ions from heat from pumps or PH use a air stone. Keeping the water a little cooler also helps.