Comment by amluto | Hacker News Reader

Comment by amluto | Hacker News Reader

> In 2023, the CDC recommended new health codes that call for "secondary disinfection" methods to keep Crypto at bay, including disinfection systems using ozone or ultraviolet light. Another possible solution is to have "single-pass" splash pads that don't recirculate water.

UV seems straightforward, even as a retrofit — a UV sterilizer is not terribly expensive or large, and it can be installed downstream of the filter without any other complication. (UV works poorly in cloudy water, which is why it goes after the filter.)

Ozone is a mess. The concentrations of ozone that disinfect are also dangerous for people, so you need a “contact chamber” to let the ozone react, and you want to avoid spraying highly ozonated water at children.

It also seems like it might be useful to sterilize the filter every night — those filters can surely end up quite full of cryptosporidium oocysts that will live for a long time. I don’t know what one would sterilize it with, though. Maybe chlorine dioxide?

Seems like there's a whole lot of UV there already.

What about iodine? It is not as volatile as chlorine.

I’ve never heard of anyone disinfecting a pool with iodine. Bromine is used sometimes. But it doesn’t seem like it would help much:

https://pubmed.ncbi.nlm.nih.gov/11990150/

In any case, IMO the volatility issue is a bit silly. Chlorine is indeed volatile, but chlorinated cyanurates are not, and one can, and should, have cyanuric acid mixed in with one’s chlorinated pool/splash pad water to “stabilize” the chlorine. (They do decrease the effecacy of the chlorine at any given concentration, but they make up for it by making it much easier to maintain an appropriate concentration.) And one can buy a (moderately expensive!) system to monitor and control, closed-loop, the chlorine concentration in the water, so maintaining an appropriate chlorine level in a public pool is not actually that hard.

The real problem here is that cryptosporidium is hard to kill.

I agree, maintaining a pool is super easy. My assumption with the splash pad is that there must be some complication introduced because of the aeration of the water, and maybe the cycle time. Aside from raising the PH, maybe it makes it tough to keep the chlorine levels up even with CYA. I wonder if it would be feasible to build a splash loop that had an intermediate tank which could maintain better control over chlorine levels for a predictable amount of time that would make sanitizing reliable.

Maintaining a pool gets less easy as the amount of gunk added increases in proportion to the volume of water. A lightly used swimming pool? Not so bad. A lightly used swimming pool with an attached spa with spillover? Barely any harder, unless you care about maintaining a nonzero chlorine residual in the hot tub. Residential hot tub that doesn't spill into a pool and gets any amount of serious use? Utterly gross without real effort.

And all of this assumes that you're just not concerned about cryptosporidium. The chlorine levels in a pool do not reliably kill cryptosporidium! So you need something like UV, which will kill it as it goes through the UV chamber.

A splash pad has huge load of junk and a small water volume. The one nice property is that almost all the exposure is to water that is fresh out of the pump and associated filters, which makes UV quite attractive.

Agreed, eliminating crypto in a typical residential pool is basically impossible. If I were sure I had a pool infected with it, I'd probably drain, disinfect as much as possible, refill, and then SLAM the pool hard with no CYA for a while. What a PITA. And that assumes the pool is the type that can be drained.

The most reliable solution, of course, is to screen the people who are going to use your pool and don't allow anyone who has even a hint of crypto symptoms to get in.

I hope that most public pools invest in a UV system. It's hard to prevent some dumbass with diarrhea from deciding today was a good day to swim anyway. Lots of those types of people in the world.

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