Can bacterial bloom impact specific gravity?

[PotatoPig]

So on a small tank I have I measure the salt weight prior to mixing, mix it in the bucket, then verify with a Refractometer. The math says 1.027, the Refractometer says ~1.027, or close enough. All good.

Mark the “fill line” on the tank, and top off to that. So tank volume is consistent.

Then I got a bacterial bloom (I’ve been struggling with this on this tank for a couple weeks now, keeps coming back despite multiple 90+% water changes and no added food, so no idea where the bacteria are getting nutrients, but they are…).

While prepping to change water I checked the salinity of the tank. Came in at 1.03.

???

Thought maybe an issue with the Refractometer, checked the DT - was 1.025 last I checked (I’m slowly raising it - LFS runs at 1.027 so and is still 1.025. Mixed up a new batch of water per salt mass and water volume, comes in right on 1.027. So Refractometer seems fine, or at least consistent with all other water.

Only thing I can think is the bacterial bloom is altering water density or affecting the result - is that possible?

/I’m slowly raising the DT salinity to match the LFS salinity of 1.027 to reduce shock to new arrivals, hence the difference between the two tanks.

 

[Rmckoy]

Evaporation …..

As water evaporates salinity will only become more concentrated .


1.026 is ideal . For reefs.
If you’re only keeping fish you could go a little lower .
Most lfs keep their fish systems lower than reef salinity .

 

[PotatoPig]

Evaporation …..

As water evaporates salinity will only become more concentrated .


1.026 is ideal . For reefs.
If you’re only keeping fish you could go a little lower .
Most lfs keep their fish systems lower than reef salinity .

For sure, but in this case I’m topping off the tank to a pre-marked line using RODI.

I was also surprised by the LFS salinity, but they mostly do corals so maybe that’s why they keep it so high.

 

[Rmckoy]

For sure, but in this case I’m topping off the tank to a pre-marked line using RODI.

I was also surprised by the LFS salinity, but they mostly do corals so maybe that’s why they keep it so high.

I don’t think bacteria affects salinity. .

Temp will bit most refractometers it will not effect .

Evap is my only thought as of now but let’s see what more experienced say