Salinity in new tank

[cindy78]

Hello...I am new to salt tanks so please be gentle. I have been cycling a 50 litre for about a fortnight after filling with purchased sea water and topping up by hand with RODI. Finally got around to testing salinity...I think it is too high? Perhaps I messed up when water changing? It reads 38PPT on Instant Ocean hydrometer? Should I panic and remove salt and add more fresh? Xenia and peppermint shimp seem ok...green star polyp has closed up.

 

[gbroadbridge]

Hello...I am new to salt tanks so please be gentle. I have been cycling a 50 litre for about a fortnight after filling with purchased sea water and topping up by hand with RODI. Finally got around to testing salinity...I think it is too high? Perhaps I messed up when water changing? It reads 38PPT on Instant Ocean hydrometer? Should I panic and remove salt and add more fresh? Xenia and peppermint shimp seem ok...green star polyp has closed up.

Before you do anything get your LFS to check the salinity of your water.

It is quite possible that your hydrometer is incorrect. Swing arm hydrometers are not very accurate and you will need to obtain a better measurement device if you plan to keep coral.

 

[Reef.]

Just to be clear, do you mean salt water rather than sea water, as they are two different things, different issues with both.

I’ll take it you mean salt water from the shop, so its either the shop sold you water that was at the wrong salinity, which is unlikely as that would cost them more money and shops don’t like spending more than they need too, in fact a lot of shops have low salinity salt water as it saves them money, so your issue is either you have not added enough rodi water or you were adding more salt water instead of plain rodi water, as its only the water that evaporates, not the salt. Or you are not using your salinity checker correctly, and to be honest the type you have is not the best.

Buy a refractometer, h20cean is a good brand, and regularly correct its calibrated correctly with 35ppm salt water.

Just to go down the rabbit hole a little deeper, a Tropic Marin hydrometer is the gold standard imo, a little awkward to use but you know the reading you get is very accurate, a good refractometer with the hydrometer is ideal, the refractometer can be used for quick readings and the hydrometer to double check your refractometer is still working as they can drift whereas the hydrometer never drifts.

 

[cindy78]

Thank you for your input. I believe it actually is ocean water. In my area we have a local shop that sells water harvested from the sea (i.e. they go off-shore to collect it in a boat). Well this is what I am being told by several people in the hobby (one who works in a competing shop that sells salt water). Crazy I know but my guess is it is ballast water. Who knows perhaps they are having a joke... humour is pretty harsh in my part of Australia. I suspect when I was filling tank I kept adding salt water after it evaporated...I was fiddling for a new days as couldn't get sump full enough for pump not to blow air, but not overflow the silly drawer (it is a strange tank...dymax IQ9 step tank). Or as you said I need a better measurement tool. I think I will take a sample into the place I bought the water and get them to test. Thanks for the recommendation on a good one...might need to save $$$...stuff is super expensive here.

 

[Reef.]

Thats why I asked as I see you are from Australia so thought it could be sea water…in that case you need to check what the salinity is of the sea water you are buying as salinity from the oceans are not all 35ppm that is only an average of all the oceans, unlikely your bought sea water is as high as 38 but it could be slightly higher than 35, so a first step is checking that so you know by how much your water has drifted from its starting point.

Take your salinity checker with you to your lfs, ask them to check its accuracy and show you have to use it correctly, they can be good but some not so good and definitely a learning curve with that type of checker.

 

[Solo McReefer]

Tropic Marin hydrometer is the gold standard i

Yes

Get one of these

And be very careful with it

 

[gbroadbridge]

Thank you for your input. I believe it actually is ocean water. In my area we have a local shop that sells water harvested from the sea (i.e. they go off-shore to collect it in a boat).

Right, in that case get the shop to measure your water for you to see if it matches.

Seawater varies a lot, but that does not really matter as long as you use the same water consistently.

My local LFS sells locally collected Seawater collected about 2km off Sydney Heads.
It's about 33ppt at the moment but wobbles up and down seasonally.

Seawater in the Mediterranean can be 39-40ppt. lol.

One of the reason's I prefer to make my own, but lots of folks around me use seawater from the LFS.

 

[Mr. Mojo Rising]

That instant ocean tester is not accurate, I would recommend a better testing tool like hanna or a refractometer, they will be much more accurate than what you have,

 

[snorklr]

along with the TM you'll need a 500ml graduated cylinder to float it in(cheap plastic) and a cheap digital thermometer whose probe you can put in with the hydrometer...specific gravity varies greatly with temperature and the TM is calibrated to 77 F ....to me its still much easier than worrying if my refractometer is calibrated correctly...seen too many threads here about them being off...

 

[Randy Holmes-Farley Verified Community Expert]

...specific gravity varies greatly with temperature and the TM is calibrated to 77 F ....to me its still much easier than worrying if my refractometer is calibrated correctly...seen too many threads here about them being off...

Just to clarify, hydrometer readings change a lot with temperature at fixed salinity. Specific gravity itself changes very little with temperature, at least in the ranges we encounter.