Drastic Salinity Changes?

[Jukas]

I recently filled my 75 gallon tank and since I had 50' of airline tubing I decided to just fill the tank directly from my RO/DI unit and then mix the salt once it was full.

Once full I started mixing salt, put in the appropriate amount and then let it agitate for over 24 hours. I then tested the salinity and find it to be just a touch over 1.025. I had intended to start moving my live rock from their holding tubs to the tank today, but I re-tested the salinity first just to be safe. This morning it's measuring 1.022.

To be sure I pulled out the calibration fluid and the refractometer is correctly calibrated to 1.025.

75 gallon tank, eshoppe 20gallon sump, quite one 4400HH return pump, 2 x Korelia 2's in the tank. Only other things I can think of is I ran my skimmer briefly (6 hours or so) to get the level set, and I have a small (1/2lb or so) bag of carbon in the sump.

Any ideas what could have caused that drastic of a drop in salinity in less than 48 hours?

 

[lcstorc]

Doesn't sound that drastic to me but it is a bit suprising to me tha it went down instead of up. The LR is likely to raise it so I wouldn't worry too much since you don't have any livestock in it yet.
I would add the rock and let it test it again in a day to two to see where you stand. With water changes and top-offs you can get a feel for how much water and salt makes what amount of change. Often you need more or less salt than it says on the salt. I always go low then test and raise it up. It is a lot easier to bring the salinity up than to bring it down.

 

[NCguy]

I hope you didn't fill the tank all the way up because you'll notice that you can't put your rocks in without the water overflowing in the floor. Not that I ever did that (crosses fingers behind back)

 

[Jukas]

I hope you didn't fill the tank all the way up because you'll notice that you can't put your rocks in without the water overflowing in the floor. Not that I ever did that (crosses fingers behind back)

I had to fill it all the way up in order to mix the saltwater or the return pump would have sucked it dry. Fortunately I was already planning on shutting off the pumps and siphoning out some of the water before I started adding the LR

 

[NCguy]

 

[msbdiving]

I have a rio powerhead that I use to drop in a bucket when I make up my water. It also helps out doing water changes instead of waiting on gravity. Just a thought.

 

[Wildreef]

I Have a 55gal. Ro/Di reserve drum , Ive tried that practice In the past by pulling off water the just adding RO water then adding salt.

Problem Is depending on your salt mix , there seems to be diffrent disolving rates for diffrent brands of sea salt mixes and/or diffrent amounts needed to acheive the same SG.

I now how ever and for the last sevral years always pull off the amount I want to change and have the same amount already made up a day ahead of time in my make up barrel.
( gives time for the salt to disolve thereby getting a true settled reading on the refraction meter )
And less chances of large fluxuations in water chemistry / SG

 

[lcstorc]

Interresting. I have a 2 60g containers where I basically do the same thing and so far have not had a problem. I do keep a pump in the salt tank 24/7 and I fill it as soon as I take water out of it so it has at least a week to mix. I don't however measure the salt. I just add what I know is not enough and go from there using a refract. I do test from the top and bottom since we draw the water out the bottom to let gravity do the work. The pump just mixes and we need it to fill one tank that is too high for gravity to take care of it.