Salt measurement - hydrometer v chemistry?

[tomfrh]

Decades ago we had a hydrometer to measure the salt levels.

Currently using clear choice salt titration kit.

How do these methods compare? Do people still use hydrometers?

I’m tempted to get one or make one, rather than use the chemistry.

 

[PoolGate]

Hydrometers are not calibrated for the low salt levels of a pool. They would give a reading but the accuracy would be questionable. I also have a refractometer that isn't calibrated for low level of salt either I tried in vain to find one. In addition, I also have an electronic salinity probe and contacted the manufacturer who again stated they were not calibrated for low salt levels. Not being calibrated for the level you are expecting means the accuracy outside the measuring devices expected range will be greater at the far ends of the scale. You could try the titration method and then compare that to your hydrometer to see how far it is off. It should remain fairly consistent.

 

[Dirk]

The Taylor K-1766 Salt Test is one of the easiest tests to do. And salt doesn't need to be tested very often, so the Kit would last a good, long time, so the expense of it is not really an issue. And salt is one of the least important levels to be concerned about. Primarily you're looking to confirm the salt level is adequate for the SWG, and most, if not all, of those work within a pretty large range of salt levels. Some have ranges that span 2000ppm give or take. So practically speaking, if the SWG will fire, then you have enough salt. And it doesn't really matter how much. If you test with titration once in a while to make sure the salt is not getting off-the-charts high, and your SWG is producing chlorine, then you're good-to-go.

So you can continue your quest for a hydrometer (I remember how easy it was to test salt in my aquarium, so it would be cool if you could test that way), but of all the things you need to track in a pool, salt is pretty much the lowest on the list...

 

[BrettClearChoiceLabs]

I've had some problems with hydrometers trying to make one and or source one. We used to bring some in but the company stopped supporting them and they would uncalibrate themselves at random. How a two piece plastic device does that is beyond me but that's what happened.

We had some manufactured and prototyped but none of them were good enough. From memory we were able to get them accurate to about 400ppm, which realistically is good enough for a pool, but over time they would become unreliable. Glass ones I believe are more reliable but also really really breakable and I don't think anyone wants glass shards near their pool!

I would love to not have the salt testing chemicals in our kits because that stuff can stain surfaces so easily including skin if you're uncoordinated enough to spill it on yourself, ask me how I know that!

 

[Dirk]

That 400ppm number keeps popping up. I believe that's the number I was given for the accuracy of both my SWG and the Taylor kit. Maybe that's as close as one can get no matter what. But again, it doesn't really matter...

 

[BrettClearChoiceLabs]

Well I know some test kits with specific test methods can get to 80ppm per drop *coughcough-oursdoes* but again whether it's strictly necessary is another matter.
For me personally, when people come to me for help with pools it's because their Chlorine, pH or CYA is out of whack. The good old trio of power

 

[Dirk]

Others here taught me that you can double the sample water (or more) and then do the math to adjust the result to increase accuracy. I never bothered to, though. My SWG is happy. I'm happy.

 

[Costas > DownUnder]

Hydrometer can be a pain - Temperature variances means that lookup tables must be used to offset the original calibration for any given set temp outside its originally calibrated temp.

1 degree Celcius change in temp can easily affect the reading by 400ppm when talking hydrometers - so not that convenient/accurate as compared to a chemical test.

Salt level is one of the least most tested variables for our pool water - Once set it does not change all that much through the year unless you exchange a lot of water.

 

[Dirk]

Yep, temperature really messes with my SWGs salt measurement. But not the Taylor test.

 

[tomfrh]

Hydrometer can be a pain - Temperature variances means that lookup tables must be used to offset the original calibration for any given set temp outside its originally calibrated temp.

1 degree Celcius change in temp can easily affect the reading by 400ppm when talking hydrometers - so not that convenient/accurate as compared to a chemical test.

Salt level is one of the least most tested variables for our pool water - Once set it does not change all that much through the year unless you exchange a lot of water.

Useful info. Thanks. I hadn't realised temperature was such a large influence.

 

[cfherrman]

I believe the 44 mil test for the Taylor is 80 ppm a drop

 

[BrettClearChoiceLabs]

We have a chart around here somewhere with temps on it and the variance from when we were working on hydrometers last time, I was surprised too when I learnt about that. Chemical tests don't care as much, which is another reason for them being so popular.

I'd personally love a working hydrometer/floating thermometer combo I think that'd be great but apparently I'm more likely to find a real live unicorn.

 

[Dirk]

I'd personally love a working hydrometer/floating thermometer combo

Oh, right. I used to have one of those for my aquarium. I suppose they worked well enough because the expected environment for them could be predicted: a tank of water that would be about the same salinity as sea water with a temperature about the same as a tropical reef, around 75-85°F, so they could calibrate the hydrometer component to give accurate salinity for that particular temperature range.

I eventually broke that one and then started using a different thermometer and a separate gizmo to measure salt, one of those narrow plastic boxes with the floating, pivoting arm in it.

I never did figure out how to use all the water testing stuff I bought and how to properly balance water in a marine tank. I've always regretted not being better at it. I bet I would be now, having learned what I've learned about balancing pool water. But one body of water at a time...

 

[tomfrh]

I’m making a hydrometer now. I need a salt reference solution. Is normal pool salt pure enough to weigh and use? What about kitchen salt?

im wondering if it has a certain percentage of water (or other things), which would mess up the solution.

 

[cfherrman]

See if you can buy a salt standard. If not make sure to use distilled water as all water has salt in it