What type of hydrometer to use for float solution – DSP 97

If you don’t know the specific gravity of your float tank solution, it makes it really difficult to make sure you’re providing an accurate float experience to every customer. Hydrometers are tools built specifically for this, but not all hydrometers are created equal. What types of hydrometers should you use and what do you need to look out for? Fortunately, Graham and Ashkahn have a lot of experience shopping for hydrometers (they break fairly easily, unfortunately) and are more than happy to share what they look for in these little measuring devices that help us make the magic happen.

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Transcription of this episode… (in case you prefer reading)

Graham: Today’s question for us from you, for us to answer to you. Is “what kind of hydrometer do you use?” “You” being “us” in this case.

Ashkahn: I don’t know the actual name of the place we get our hydrometer’s from.

Graham: Isn’t it Scientific …

Ashkahn: Scientific American. It used to be, I don’t know if we still are exactly getting them from there. We might get them online from somewhere.  Here is what you are looking for, when you’re looking for a hydrometer. First of all, you’re looking for a specific gravity hydrometer. So there’s nothing in there that’s specifically about the salt water or anything like that. You’re not looking for like an Epsom Salt hydrometer or anything. You’re just looking for something that measures specific gravity.

Graham: And within a certain range. Specific gravity can be pretty broad. You know even lead has like a specific gravity of ten or something like that right?

Ashkahn: And there’s hydrometers for different applications like brewing beer and things like that.

Graham: Battery acid is another common one.

Ashkahn: But most of those are not actually in the right ranges for what you’re looking for. So, typically you’re looking on some sort of company or website that does make scientific equipment. That’s the most common place you’re going to be able to find these on websites or somewhere in town or somewhere like that. Is that scientific equipment company. Basically you’re looking for something that is the range of your float tank. People have their float tank sitting anywhere from maybe 1.24 specific gravity to like 1.29 or something. So, it’s not always easy finding exactly the right range on the hydrometer. Sometimes they go from 1.2 to 1.3 which is okay except that if you ever go above 1.3 then it’s kind of nice to have something that shows you the higher numbers but you never really want to be above there anyway and you kind of want to be balancing down.

Graham: If you could just magically produce a hydrometer at the right range, what do you think is the ideal range to be able to show on it?

Ashkahn: Basically there’s two different ways that I think are both pretty nice. One is just the single hydrometer that would show you your full range. Like if you had like a 1.2 to 1.33 hydrometer would be pretty great. The other one is like the smaller the range is, the easier it is to use because all the numbers and lines and everything are bigger. So the other option and we’ve been done this sometimes when they’ve been out of other types of hydrometer is you can get one that’s like a 1.25 to 1.3 and that’s going to serve your normal use. Every time that you’re checking levels and filling up. But then, you’re going to need another hydrometer with a bigger range when you’re actually filling a float tank up from scratch or something like that.

Graham: Uh huh.

Ashkahn: And another really common range I see all the time is 1.2 to 1.42.  So, we’ve done that before too. But I think now we have one … I’ll have to check what we have. We break them so often that it’s hard to keep up sometimes.

Graham: Yeah, we recommend getting fragile glass hydrometers.

Ashkahn: So, a couple more things to know about hydrometers. There is one other application that I know of so far that does conveniently happen to be in the same range as float tanks. Which is what Graham was mentioning: battery acid.

Graham: Yep.

Ashkahn: They keep the specific gravity of battery acid at, actually like shockingly the right range. If you buy a little battery acid hydrometer it even usually has a little green range on it. Which happens to line up with what the good range in a float tank is. Which is really funny.

Graham: So the weird thing with those, despite specific gravity being something that should stay constant is when we’ve gotten the battery acid ones to try out, because a lot of them are you know, you don’t want to be touching battery acid with your bare hand, so they’re kind of made for caustic solutions even. Which is, which is cool.

Ashkahn: Yep.

Graham: But they haven’t given us the accuracy of the other hydrometer and in fact seem, like not, not even close to being able to kind of produce that same level of trustworthy results. When I’ve used just a little again like plastic, handheld, generic battery acid tester.

Ashkahn: Right. So they’re nice in the sense that they’re usually like a dollar. And they’re made of plastic and they have like a turkey baster type mechanism.

Graham: Yeah.

Ashkahn: Which is convenient but we’ve found some that, I don’t know why, but weren’t working at all. And the ones that even do work well is just the specificity you’re getting out of them is not anywhere like where you’re getting out of these scientific glass hydrometers. So we haven’t personally really found them to be useful enough to actually use in our float center. So we go with the, you know, $35/$40 glass ones that you get.

A couple other things to know about hydrometers. One is, you know, you’re taking a sample of the water in your tank into some sort of graduated or non-graduated cylinder and then putting the hydrometer in there to see the levels. The other thing to know is that if that cylinder is too tight that can actually cause the hydrometer reading to be inaccurate. You need to actually have a graduated cylinder that provides a little bit of space around your hydrometer otherwise I think the surface tension of the water kind of like creates a false level that you see there. If the size is too close together. So getting a nice well sized one is going to make your levels more accurate.

Graham: And a note on that too. Because we’re using glass precision hydrometers, we don’t want to put those inside the float tank. So, that’s the reason that we’re pulling out the water to test in the first place. Rather than just letting the hydrometer float in the float tank because the idea of breaking glass inside your float tank just sounds like such a potentially awful, expensive mistake. That there is no way we would even hold a glass object over the body of a float tank. That sounds just too risky so that’s why we’re pulling it out and putting it into a smaller container and floating it there.

Ashkahn: And it’s easier to read, otherwise you have to like lean your face to the water level.

Graham: That’s what all the cool kids are doing.

Ashkahn: The other thing to know about hydrometers and this is more just like a useless piece of information.

Graham: They were invented by Mr. Hydrometer. Back in the late 1700’s.

Ashkahn: All the ones that I’ve ever seen just on these websites are usually calibrated for I think it’s 65 degrees Fahrenheit so they are based off of a temperature. And I’ve never attempted to do anything other than just buy those ones and think it’s probably fine. I’m pretty sure everybody in the industry and all these numbers are basing all these conversations off of, is using hydrometers that are calibrated for a lower temperature than our float tanks actually are. My guess is it’s just probably small enough of a difference and the actual amount of salt in a float tank is not as exact of a science necessary to care about that.

Graham: Probably like the error in us reading the hydrometer is more than the difference in that small amount of temperature.

Ashkahn: Or maybe it’s more and we just don’t know because we’ve never had anyone use an accurate one to see what the difference is.

Graham: Along those lines too, will actually be affected by your altitude and the air pressure on it so your readings will be slightly different at sea level in California than they will in Colorado too.

Ashkahn: But at the end of the day it doesn’t really matter like the levels you’re trying to get your float tanks to have enough wiggle room in them that I don’t think you really care too much about little margins of error and stuff like that. And buy multiple.

Graham: And name them and put googly eyes on them.

Ashkahn: Because you’re going to break them. You can’t put googly eyes on the hydrometer. I think that would probably mess with it’s calibration.

Graham: I guess that’s another thing. We do have nice padded cases.

Ashkahn: Yeah.

Graham: For them, that are essentially like PVC tubes that have foam in them.

Ashkahn: And they sell those, that’s like a product you can buy usually from the same website you’ll find a hydrometer.

Graham: You’ll have to attach your own googly eyes but it doesn’t take very long and they’re pretty inexpensive.

Ashkahn: So yeah, that sums that up.

Graham: Alright, thanks everyone! And especially the person who sent us that question. And if you want to send us your own, go to floattanksolutions.com/podcast.

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