The moment I found out my refractometer was lying to me for 8 months

So I've been keeping saltwater for about 2 years now. My corals always looked ok but not great. Growth was slow, colors were meh. I checked salinity every week with my refractometer and it always read 1.025. Then my buddy brought his calibration fluid over last Saturday. We tested mine and it was reading 1.025 when the water was actually 1.030. Turns out I never recalibrated after I dropped it on the floor back in March. The needle bent just enough to throw everything off. I felt like an idiot. Has anyone else trusted their gear for way too long without double checking it?

2 comments

2 Comments

colemartinez2d ago

People really sleep on the temperature side of this too. Your refractometer measures water based on how light bends through it, and that changes with temperature. If you calibrated it at 75 degrees but your tank runs at 80, you're already off before you even start. A bent needle makes it way worse, but a lot of guys never even check if their reading stays the same when the water warms up. Most cheap refractometers have Automatic Temperature Compensation but it only works in a narrow range. I would bet a good chunk of your 8 months of wrong readings was from the temp swing, not just the drop. Get a handheld digital or at least test your water at the exact same temp every time. That way you only have to chase one variable instead of two.

leohart2d ago

Most freshwater tanks sit pretty steady within a degree or two, and the average room temp doesn't swing that much between seasons. I've run the same cheap plastic refractometer for years and only recalibrate every few months, and my readings have never drifted more than a point off my LFS's digital unit. If you're keeping a reef tank with delicate inverts, sure, chase that temp variable. But for most of us doing softies or fish-only, a 5 degree swing isn't going to ruin your salinity numbers like people make it sound.