Any tips on cleaning a tank?

[SouthernSharktoothDiver]

Hey all,
A bad fill put some water in two of my AL 80's a while ago. One I caught right away, the other I kinda just put off because it was a pain to deal with and I was really busy. Anyway, I got the first one rolled a week or two after noticing it was direct, but I needed to use the other one (it was still under pressure) so I just let it sit for a month or two and then air dried it for a while.

To some of you, this may seem stupid, and indeed, I'm starting to think that was the case, but in my defense, the guy that did the other one's tumbling said it'd be fine and wouldn't hurt it any, so I figured he'd know, right? So, I let the water in the one that's still dirty air dry and all that, and the tank's got this weird bacterial film looking thing in the bottom. I can try to get a pic if anyone wants one. I took it to the local hydro place for a tumble (not where I took the first one. That guy's way far out of my way and I was going to the hydro place anyway and the guy who cleaned the last one said he was just gonna hit it with blue gold and tumble it.)

Now the guy at the hydro place is real nice (and good at customer service) and offered to tumble it on a trial basis since I was getting three other tanks hydro'ed. If it didn't work, no charge on the tumble. Welp, come to find out, the tumble didn't work. It looks about the same as it did before, same filmy look. So, what do I do now? I could go to the other guy, but I suspect he won't be so open to only getting paid if it works (and like, nor should he, necessarily, but also, I don't wanna spend $30 when I don't think it will work).

Should I try getting it O2 cleaned? or should I just say screw it, if rolling with abrasion media in it didn't loosen anything, it probably won't hurt me? Or, third option, there's another guy that an older diver I know gets his fills from who does some sort of tank cleaning, I could see if he has any new ideas.

So, yeah, thoughts? I bought this tank brand new, a year ago, and I'm pissed that it's mucked up, but I got fills from several people, so idk who's responsible and I'm not willing to go around accusing fill guys without knowing who did it.

 

[OMyMyOHellYes]

Who is doign your VIPs annually? Did they have any remark?

Does it have a smell? Is the film colored green (or just colored in any case) Is it discolored/stained Al (usually dark)? Ring where water would have puddled? Possibly a film of Al2O3? A uniform coating of fine Al2O3 inside a tank can sometimes appear a sort of semi-opaque milky haze over what would otherwise be the shiny bare aluminum (which is OK, if not desirable as that fine layer can inhibit further oxidation of the metal), but I would suspect a decent tumble would kinda clean that off...

I usually go to a whip (either scotch pad or fine wire) before going to a tumble, but htat's me. But a run at it with some detergent like Blue Gold and tumbling media may be OK - note Blue Gold is essentially a de-greaser more for O2 cleaning, but don't see that it would hurt anything. Any chance that there were other contaminants in the water (oil?)? Do you know with what/how the hydro shop did the more recent tumble? Outside of doing an actual hydrostatic pressure test, I don't really trust MY local hydro shops to know a lot about scuba bottles (they really don't - they test fire extinguisher bottles and industrial gas bottles primarily). YMMV.

 

[SouthernSharktoothDiver]

So, to try and answer what questions I can in order:

This tank was VIP'd by a dive shop a few hours away where I used to live, almost exactly a year ago. Otherwise, I don't have a regular VIP guy yet. Just been running off the hydro place's VIP and getting fills from a guy that doesn't require them. But yeah, no remarks from them.

It smelled kind of dank initially, when it was wet. Kinda musty. No long smells like anything much except aluminum. It's a dark looking stain, kinda like the mold on a shower curtain. I'll see if I can get a light down there for a pic if you think that would help. It does appear to be where the water puddled. AlO2 is generally white, right? This doesn't look like the oxide I'm seen before, but I have little experience with that and scuba tanks.

It's entirely possible there were other contaminants, since clearly the pump wasn't working right, but the air tasted fine (I dove off it several times before I knew it had water in it, judging by the timelines of when/where I got my fills and how long it looked like the water had been in there.

the hydro place used an abrasive bead media, and I know they alternate through increasing sizes in several cycles over the course of several hours. Since the issue was on the bottom of the tank, they angled it to hit that area. Otherwise, I'm not sure. And yeah, they're pretty open about not knowing a ton about scuba, I just thought it was worth a shot since they had the gear for it and I was going there anyway.

What do you think? Am I overthinking things? Should I just dive it as is?

 

[OMyMyOHellYes]

Yeah Al2O3 is usually a whitish tone. But water can make dark stains on Al. I'd be interested in seeing a pic from a curiosity standpoint, but I wouldn't be comfortable expressing any opinion without seeing it in person. That's why I asked about a qualified VIP technician (hopefully somebody with current recognized training through PSI/PCI - there are others like SDI/TDI or maybe Cylinder Training Service - but I am not familiar with their courses /resources and can't express any opinion on their qualifications). A trip to a qualified VIP tech is really going to be the best source for an answer.

If your local shop does not maintain recognized qualification, you might want to reach out directly to PSI/PCI and ask for a referral to an inspector local to you. Note that they have discontinued maintaining their online listing of inspectors, but I'm guessing a call or email might be useful. They're located outside Greensboro, NC so it's EDT business hours.

 

[happy-diver]

Other than not bothering about it I would tape some cloth on to the end of a stick and spin it in a drill

Rumbling an aluminium cylinder yeah, why, and I don't see much action with the machine on an angle



Go for broke!

 

[SouthernSharktoothDiver]

@OMyMyOHellYes I'll see if I can't snap one tomorrow. As for a qualified VIP technician....I don't honestly know. I've had enough contradictory or liability conscious, wishy-washy opinions from people who do VIP's on previous tank issues in the short time I've been doing this that I don't put much stock in any of the ones I've come across. It's honestly given me the opinion that the VIP is simply a way for the dive shop to make $10-20 off you quick, but then again, that's from a handful of people in non-dive intensive areas, so sampling is important.

I'm eastern time too, so I might call PSI/PCI and see what they say. I'm also going to see an older diver that knows a lot about this stuff and see what he'll think. Knowing him, he'll saw I'm overthinking it and say that tanks just get like that sometimes, but it will make me feel better. He's been doing this long enough and often enough that if his way was all that dangerous he'd be dead by now.

@happy-diver I'll take that under advisement.

 

[Endler's]

At a minimum...

shouldn't you use something like this?

 

[Capt Jim Wyatt]

 

[flymolo]

Usually when you tumble aluminum tanks you fill them at least half way with glass beads and then a certain amount of cleaning solution, and top off with water, cap them off and put them on a tumbler for about 30-45 minutes or so. You want enough beads and water in there so that the tumbling will cover the entire interior surface of the tanks.

More abrasive media, like ceramic beads, I’ve typically used in steel tanks, not aluminum.

I wonder if the hydro place used any kind of cleaner in the tanks when they tumbled them?

 

[GJC]

My first thoughts were that it is mold, oil, or some other chemical that stained the surface.

I would try Simple Green first to see if that removes any oil or mold.
Depending on what it looked like after that, I might just leave it if it looked like a stain. If not, I might try to see if a probe could scratch it. If it scratches off, gently using a bottom brush might remove it.