After watching the video and reading this thread I'd like to make the following points.
The use of tap water may be fine, if, and this is a very big if, you have very high quality tap water to start with. It has been my experience that most of us do not have such high quality water. This means we need RO/DI water or equivalent to get decent results. In other words, we what to control or prevent algae blooms, and we want to maintain the highest possible water quality for corals.
In my personal experience, I found that while the town I was in had good quality tap water, by drinking standards, and even by FW aquarium standards, it came up short when using it for a SW reef system. Switching to RO water made a quantum improvement in the system. Not that this was just RO water, not RO/DI and that this was a very early reef system.
I'll leave it to each individual to decide if they need RO/DI water or not. However, I would highly recommend it's use.
The other point where I take issue with the videos is that by the guys on admission he's never used a refractometer, and furthermore can't explain how it works, and also doesn't even get the price correct. In other words, he tells us that he's got no idea what he's talking about and then goes on to give his opinion. In my opinion, as soon as he did that he completely destroys his credibility.
Again, my personal experience. I used the glass floating hydrometers for years, and had also used the swing arm types for years. Once I got a refractometer, I found that I finally got accurate readings, and could toss all the other junk. I also found that a refractometer can also be used to test many different small amounts of water. This is real nice when you get a large box of corals, and you need to do know where you stand. I know I have to spend a lot longer on the acclimation process if the SG difference is .005 than I do if it's only .001.
Keep in mind that a slightly different density makes a big different in readings such as calcium and magnesium. For example, if your water is off by .002, reading 1.023 instead of 1.025 you are off by 8%. This means that that your calcium reading will be skewed by a similar amount. in other words, assuming you would normal want a reading of 400 at 1.025, your reading at 1.023 reading would only be about 370. You really would not want to supplement calcium, when your real problem is SG.
I would consider a refractometer a very nice thing to have, but not critical.
Bottom line, I do not feel the money spent by the original poster was waisted.
In addition, if the original poster still does feel his money was wasted, he still learned a valuable lesson. That is, do your research on the product before you spend your money. Also, be somewhat glad it was only on a $100 or so RO unit, which can always be resold, and not on something extremely expensive, such as a new lighting fixture, or that big investment that was going to make your rich overnight.
:hug1: