I am going to guess that when you say you keep your tank at 0.24 that you mean 1.024 SG. Otherwise I don't know what 0.24 salinity is???
I would not buy this refractometer for aquarium saltwater. It measures percent at a very high level. Our tanks are kept at or about 1.026 SG, or 35 parts per thousand, which is equal to 3.5 percent. If you look at that scale they provide in the link, you will see that 3.5 percent is at the lower end of the scale. With such a large scale, your accuracy would be crap!
You can still find the correct refractometers on ebay....the two I've purchased came from there....and are just fine. Just make sure you get the correct calibration fluid....53mS solution.
EDIT TO ADD: I'm not saying, "buy
THIS one," but I'm sure it's just fine....I just wanted to show you an example of the scale you should be looking for. And again, I'm sure this one example of hundreds is just fine.