I have two, one that floats in the aquriuam and an instand ocean one that u fill up with water and the needle moves, they both give me very different readings which one should I trust. I know it's been suggest i get one of those better ones off of ebay but at this time I don't really want to invest in one...
what should i do
Hydrometers
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nmonks
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The reason you get different readings may be that your are floating the hydrometer in the aquarium. This will not work! Put water into a glass jar of some kind (e.g. a pickle jar) that is big enough for the hydrometer to float in. What you are improvising is a measuring cylinder, which is how hydrometers are used in labs. Fill with water, then float the hydrometer. Leave it sitting for a minute. The water has to be completely steady: all currents, including thermal currents, will mess up the reading.
Make sure you read the floating hydrometer properly. Ignore the meniscus (the upward curve of water going up the stem of the hydrometer). Make sure you clean the hydrometer afterwards.
All hydrometers are 100% accurate at one temperature... the problem is that temperature may not be what you are using it at. Check the device in question. Most are calibrated to work at 20-25C.
If we're talking brackish water fish, and you don't have anything sensitive (e.g. plants) then frankly it couldn't matter less what the salinity is provided you are consistent and using the same hydrometer from week to week. Even if SG 1.010 is "really" SG 1.012, your fish won't mind and the filter won't mind because the salinity of the water will be constant (though admittedly, constantly wrong).
There's no guarantees that hobbyist refractometers are any more accurate or consistent than old fashioned floating hydrometers. Lab-grade refractometers cost $100s-$1000s. I'm not wild about swing arm hydrometers. IMHO, a cheap floating hydrometer works consistently and has no moving parts to go wrong. Swing-arms depend on the pivoting point staying clean and loose, and I suspect after a while salt and lime prevents that by building up as a deposit that causes friction. Try washing it out with vinegar and then trying again.
Cheers, Neale
Make sure you read the floating hydrometer properly. Ignore the meniscus (the upward curve of water going up the stem of the hydrometer). Make sure you clean the hydrometer afterwards.
All hydrometers are 100% accurate at one temperature... the problem is that temperature may not be what you are using it at. Check the device in question. Most are calibrated to work at 20-25C.
If we're talking brackish water fish, and you don't have anything sensitive (e.g. plants) then frankly it couldn't matter less what the salinity is provided you are consistent and using the same hydrometer from week to week. Even if SG 1.010 is "really" SG 1.012, your fish won't mind and the filter won't mind because the salinity of the water will be constant (though admittedly, constantly wrong).
There's no guarantees that hobbyist refractometers are any more accurate or consistent than old fashioned floating hydrometers. Lab-grade refractometers cost $100s-$1000s. I'm not wild about swing arm hydrometers. IMHO, a cheap floating hydrometer works consistently and has no moving parts to go wrong. Swing-arms depend on the pivoting point staying clean and loose, and I suspect after a while salt and lime prevents that by building up as a deposit that causes friction. Try washing it out with vinegar and then trying again.
Cheers, Neale