Saltwater Mixing Questions

msderganc · Apr 13, 2017

Hi Randy,

A couple of questions for you:

1. When mixing saltwater, would rapid or violent water movement cause precipitation? Is there an upper bound to the turnover of a mixing container? Typical setups have water being pulled from the bottom of a container, moving through a pump and falling back into the top of the container above the level of the water (breaking the surface). Would that cause any problems with salt mixing?

2. In terms of aerating the water, is there any difference between an airstone and the above method? Would one be better?

Thanks,
Matt

jason2459 · Apr 13, 2017

IF there is a pump in contact with the water that is creating the very rapid or violent water movement then it's most likely causing some heat which locally at least could cause some precipitation. I did a little experiment trying to force a precipitation event and gradually increased the temp of the water. My pump and heater formed precipitation well before anywhere else. Ended up ruining the pump by the end...

Why do you want to aerate the water? Do you plan to add an acid? Or a salt with organics in it and plan to hold on to it for a while?

msderganc · Apr 13, 2017

jason2459 said:
IF there is a pump in contact with the water that is creating the very rapid or violent water movement then it's most likely causing some heat which locally at least could cause some precipitation. I did a little experiment trying to force a precipitation event and gradually increased the temp of the water. My pump and heater formed precipitation well before anywhere else. Ended up ruining the pump by the end...

Why do you want to aerate the water? Do you plan to add an acid? Or a salt with organics in it and plan to hold on to it for a while?

Well, we're having a discussion about this on a local FB group and I was curious as to whether there was any science supporting one way or the other. What temperature was causing precipitation?

I personally would aerate to raise pH (this water was in a holding container) before an automated water change.

Randy Holmes-Farley · Apr 13, 2017

As the temperature of seawater is raised, calcium carbonate becomes less soluble, so is more likely to precipitate.

Aside from heating, violent agitation won't increase precipitation from seawater. I'm not certain what methods aerate the fastest, but I'd guess an airstone is slower than violent agitation because the container top surface area is likely more than the bubble surface area in many cases, there's no stagnation of the air itself above the container the way there might be in a bubble, and the moving water itself brings unaerated water to the air surface faster.

Faster mixing may cause less likelihood of local precipitation near dissolving sodium bicarbonate/carbonate or calcium chloride particles.

I never thought aeration of new water for slow automatic water changes was needed beyond initial mixing.