Cheap Refractometers and next step

BrightReefer · 2026-08-13T12:09:06-0400

My recent failed attempt with a Duncan coral had me second guessing my salinity that is apparently 33-34ppt. I am using what Amazon says is a seawater salinity refractometer ( https://a.co/d/036fkO3T)

Going over Randy’s refractometer article how they work. I was looking into a slope issue since I calibrated it to 0 with distilled water. Would I assume since it’s a cheap “seawater” refractometer that it is most Likely a brine model in reality?

So I order a small kitchen scale and made Randy’s DIY solution. When I measured it, I got about 37ppt. Made a second batch, it was about 36.5 ppt.

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So I would say I’m doing it correctly. If that is the case would I use the DIY adjust to 35ppt and carry on?

I haven’t made any decisions yet on changing my salinity in the tank. It will almost be 2 years old so I didn’t want to shock anything. Just looking to learn and next steps. It would make sense if my salinity is wrong. As my alk measures 6.9-7.3 on average.
Hope My ramble makes sense TIA!

get-salty · 2026-08-13T12:17:03-0400

thats the refractometer ive been using for nearly 5yrs. i calibrate it with BRS solution as well as RO water and i get consistent #s for the last yrs.

idk and nvr have used Randys solution but i can tell you this..
Consistency is key.
if your water is going strong and stable for nearly 2 yrs. i wouldnt change a thing just bc a coral didnt make it.
sometimes corals will just go.. even on a 10yr tank.

exnisstech · 2026-08-13T12:46:05-0400

I've been using the same one for 10 years but have never calibrated it with RO. I've only calibrated with off the shelf fluid and the last few years Randy's solution. I now use a TM hydrometer for mixing water then I just use that water to check calibration.