Mixing Salt - Testing for Salinity

[RaymondL]

After mixing a fresh batch of saltwater, I measure the salinity and it's at 1.026 - with a powerhead still on, I leave it over night, and the next afternoon, the salinity dropped to 1.024! I'd think it would be the other way around, but not in my case. I used the same instrument to measure the salinity, and also I tend to verify again with a floating hydrometer, and the reading holds true.

Is it normal for salinity to drop?

 

[Lavey29]

After mixing a fresh batch of saltwater, I measure the salinity and it's at 1.026 - with a powerhead still on, I leave it over night, and the next afternoon, the salinity dropped to 1.024! I'd think it would be the other way around, but not in my case. I used the same instrument to measure the salinity, and also I tend to verify again with a floating hydrometer, and the reading holds true.

Is it normal for salinity to drop?

Certain salt brands say not to mix with powerhead for more then 2 hours. Maybe that has something to do with it. I use a circulation pump in a brute for 1.5 hours to mix salt water up.

 

[Fish Styx]

What temperature was the water when you mixed it, vs. when you took the reading the next day? Specific gravity / salinity readings are temperature dependent. If your methodology doesn't account for that, and isn't compensated, it could very well explain the different measurements.

 

[RaymondL]

I'm using Instant Ocean Reef (using up the last batch and will switch out as I"m not too happy with the salt anyways).

I'm mixing at room temperature....I made a 5 Gal bucket of RODI, and didn't get the chance to mix the salt until the day after, so the temperature was the same for 3 days as is.

Weird.

 

[Fish Styx]

I'm using Instant Ocean Reef (using up the last batch and will switch out as I"m not too happy with the salt anyways).

I'm mixing at room temperature....I made a 5 Gal bucket of RODI, and didn't get the chance to mix the salt until the day after, so the temperature was the same for 3 days as is.

Weird.

Room temp does fluxuate. That being said, when mixing, pumps add heat to the water. That could be your variation.

 

[mike550]

Following up on @Fish Styx how are you measuring salinity? Temperature affects salinity. Some probes compensate for temperature others don’t.

 

[mattdg]

I mix IO into a 60 gallon drum every month or so and let the powerhead mix for 12 hours / over night. Not a problem. One thought is your powerhead is heating up the SW, causing the perceived drop in SG.

An idea is to heat your bin up to display tank temperature and adjust the SG to where you want it. Then let it cool down to your average room temp and take another reading. This will be your SG target, for mixing room temperature water.

 

[14 foot reef]

If you’re using apex with temp compensation then temp doesn't affect salinity reading. This is a 7 day period from 67 degree water to 77 degree water. Notice salinity reading doesn’t change