Does suspended sand cause increased SG?

[Strangelove]

I'm setting up my new reef tank and added sand a few days ago. The specific gravity was good prior to the addition of sand. Now that my water is cloudy with sand the SG is much higher.

Am I correct in assuming that the sand is causing this increase and that the sg will decrease as the sand settles completely?

Thanks,

Gene

[Randy Holmes-Farley]

Gene:

Good question!

The answer is that anything suspended or dissolved in the water will impact the specific gravity measured with a hydrometer. The simple reason is that hydrometers float at a level such that the weight of the displaced water equals the weight of the hydrometer. If the water has sand (denser than water) suspended in it, then the water + sand being displaced by the hydrometer weighs more than the water alone, and you can get a false reading (too high of a sg).

How big this effect is will depend on how much is suspended, and in most cases I'd expect no detectable impact at all. In really cloudy water, however, the effect might be significant.

Another possible effect is that the solids might be sticking to the hydrometer, weighing it down, and making the water look "light" (too low of sg).

I'd wait a few days and see what happens, but you could take some out now, put it in a calm container to settle, and remeasure.

What kind of hydrometer are you using?

[Strangelove]

Thanks for the reply. I'm using the "cadillac" of hydrometers, the Seatest.:)

The water is much more clear today since the rock I added as putting enough protein in the water to precipitate or bind the sand dust. Still at 1.028, though. Might have to add some free water.

[Randy Holmes-Farley]

If my tank read 1.028 with a SeaTest, I'd bring it down to about 35 ppt. My SeaTest reads a bit low (35 ppt reads as 34-34.5 ppt). I don't really understand how adding sand could drive it up and make it stay up!

[Strangelove]

I don't really understand it either, unless there is salt in the Southdown sand that I added.

I guess I'd better get in there and chenge some water.

Just when I think I have all my ducks in a row somebody moves the pond:rolleyes: .

[chris_h]

Did you remove the water that the sand displaced? If you just put sand in and do not remove any water, the salinity will go up due to evaporatio.