Having trouble measuring SG

[TobiasRieper]

Im having trouble getting an accurate reading with my hydrometer. Heres the problem.

Last night I took one gallon of water in a bucket and added salt till the hydrometer said 1.004. I let it sit over night with a powerhead running in the bucket.
A couple of hours ago I checked the SG and the hydrometer said 1.008. Double from last night when I added the salt.

I cant seem to get an accurate reading, I made sure I tapped the hydrometer and made sure there were no bubbles in it... Am I doing something wrong?

[Troender]

Was there any difference in the temperature of the water? That will affect the readings.

[TobiasRieper]

Was there any difference in the temperature of the water? That will affect the readings.

I added cold water from the tap then added salt and let it sit in room temperature over night. So im not sure what temperature difference was from last night to this evening.

Should I let the water sit for awhile in room temperature then try adding salt? Should I use tank water?

[Dadof4]

I use room temp water for mixing then bring it up to tank temp before adding. Some hydrometers say they are only accurate within a certain temp range, you may want to check yours. One other thing I do too is wait an hour before I measure SG, give the salt time to completely dissolve and mix. Then I adjust from there.

[Troender]

I never test the water until it has room temperature, or the temperature is the same as in the tank. But I know how much salt to use, so I just test to control that it is right before pouring the water into the tank.

I would wait with adding the salt until the water has room temperature. I either do that, or use warm water from the tap. That last thing is not recommended, as there can be some issues with using warm water from the tap (I know my water well enough to do it - I've never had issues with it. But that can differ from house to house).

If you can find money to buy it, I would recommend buying a reflektometer. I didn't know how much easier it was until I bought one. I find it much easier to get a reliable reading than from a hydrometer.

[TobiasRieper]

Thanks for the replies everyone

I think what I will do is use tank water (77 degrees f), add salt and let it mix with a powerhead for an hour then see what the hydrometer says. Ill post back later to tell you the results.

*btw my hydrometer is from instant ocean. Is that a good one? And what is a reflektometer Troender?

[edmlfc1]

Here's a refractometer:
http://www.drsfostersmith.com/product/p ... atid=10490

You can also get one cheaper on ebay. And yes temp will change the sg in the water. Also if the salt is not totally disolved the sg will change. I would mix the salt with water let it sit overnight to disolve and match the temp then check it before adding to the tank. If you have a tub or an old tank that you use all the time for mixing you will know exactly how much you need each time. It gets eaiser with pratice.

[Troender]

Sorry, I meant refractometer. My fingers don't cooperate tonigh.

[Pufferpunk]

I always mix overnight at the same temp as the tank.

[frenchie]

what is the reasoning for mixing overnight? I have been mixing with water the same temp as the tank and it maybe sits 10min before it goes back in, and haven't had any problems. Will this cause problems in the future?

[Pufferpunk]

There are many minerals in marine salt that do not dissolve quickly & need about 24 hours to dissolve totally. That being said, I premix all the SW for my marine tanks ovewrnight at the miminum but I always have a 33g bucket of heated mixed salt on hand for emergencies. For my low-end BW tank, I know exactly how much salt it takes to bring the SG to 1.005, after a 50% WC & I add it onto the HOB filter as I'm filling the tank.