Hi, thanks for reply, I’m sure everyone’s tap water varies greatly, when I was a newbie to marine I spent out on all the usual waste of money gimmicks but upon running out of tester fluid I used tap water as last ditch thing, then when I got more fluid compared results and there was no difference, I also follow Randys recipe for making Calc, Alk and Mag additives and have used these for 5 years, don’t follow blindly like sheep try things and compare, lots of this hobby is for people to make money
I had a similar experience - I only tried two bottles of commercial solution, but both were newly opened, within date, and *way* off. One was ~30ppt and one was ~40ppt if I recall correctly. So from my experience, you are better off calibrating to RO or distilled than trusting a commercial cal solution.Calibration solution can also be off. I bought a bottle off Amazon or eBay. Bottle was sealed and well within the expiration date. I forget how much it was off by and the brand but it was for sure off. Now I just test the water I get from my lfs whenever I get a new fish or coral and calibrate off of that. Figure with thousands more invested in livestock and replacing lost water everyday they keep a very close eye on it.
This. Do this. That is what I used to get my estimates on how far off the commercial solutions were. While I don't necessarily trust my solution to be spot on, (e.g- I did not calibrate my scale), after calibrating my refractometer to that, it said my newly mixed batch of saltwater (which I had mixed by mass) was 35ppt... so I see those as two independent methods cross checking each other.Better make your calibration liquid with randy's recipe or buy a precision hydrometer from tropic marin
I just bought a back-up IO swing arm and it was reading way off, and was dirty with calcium build up. I just finished acid washing it and at 33ppt it was reading almost 39+ppt. So I broke out some JBWeld 2 part epoxy and mixed up a razor thin slice and added a little weight to the arm to get it reading properly. (My other has been sampled water from the LFS and compared to other tools and it stays reliable.I’ll never waste my time and money on a refractometer. They get no respect but my IO brand swingarm consistently agrees with my fancy tropic Marin hydrometer.