Hot Tub Chemistry...ahhhh...finally Got It Right

[Tanakaba]

Hi All,

Nice to find a forum devoted to hot tub water chemistry.

My wife and I purchased a 300 gallon hot tub 3 years ago, and we have it on our back porch in upstate NY. We love it and use it all year.

Cutting to the chase, I started off using stabilized dichlor with Clearwater Blue, Oxyspa and the tub's ozonator. I was religious about chasing pH, alkalinity, copper, residual chlorine, etc., and could not figure out why, after 30 days or so, I would begin having bioscum, foaming, clouding and itchy skin on arms and legs behind the elbows and knees. I was following all instructions religiously.

Then I did some web cruising and found that the cyanuric acid (CYA) that is meant to UV stabilize the chlorine severely diminishes chlorine's sanitizing capability as the CYA builds up. We rarely use our hot tub during the daylight hours, so we really didn't need the stabilizer, but couldn't find an unstabilized chlorine product locally.

So I purchased test strip that had CYA on it, and actually began using CYA levels, foaming frequency and any signs of itchy skin to determine when to dump the tub. Primitive to say the least.

I went back to the web and dug deeper for a non-stabilized chlorine product and how to properly use it. The first thing I changed was to nicely ask my wife to back off on the skin care products on nights that we are going to use the tub. That was tough, but we humidify the whole house now and that has helped her to use much less skin cream.

My next move was to an unstabilized 29% lithium chlorite dry granules with 35% active chlorine . Go easy, as you need less than one ounce to sanitize a 300 gallon hot tub. In has very little chlorine odor, dissolves instantly but the chlorine residual drops sharply after doing its job. Some people say that it's expensive. A 5 lb jug has lasted me from last June until now, and has another two months worth of product remaining.

I stopped using dichlor except for when I put new water in the tub. I use it then for the first few sanitizations while monitoring CYA. When the CYA hits the minimum ppm, I stop using the dichlor. This recommendation came from the web, as it leaves some stabilizer in the tub.

The next thing I did was to stop using the Oxyspa. Haven't used it in over a year.

I continue to use the Clearwater Blue kit, which is a copper ion mild sanitizer and mild algicide. The Blue keeps working after the lithium hypochlorite residual drops off.

I also upgraded my ozonator to a bigger unit.

Here's the recipe that has been working for the last year and gives us a long-lasting, clear, clean and non-itchy hot tub (the wife thinks I'm a hero!):

1. Fill hot tub with city water and use the Clearwater Blue product per instructions. There's a filter prep step with it, so read the instructions carefully.
2. Use about half an ounce of the above lithium hypochlorite product after each soak, and turn the jets on high with no air to mix for 10 min. Make sure you leave your air OFF when the tube is idle, as it can affect water pH.
3. Use a pleated, antibacterial tub filter, and take it out and clean EACH PLEAT by hand under your shower head or sink with sprayer nozzle no less than once per month. Let filter dry and rotate in another, clean filter. This is important...you don't want to leave even one pleat with scum in it that could hold hibernating bacteria even when the filter is dried out. This effort alone prevents re-innoculating the hot tub with bacteria. I no longer use a trisodium phosphate filter soak.
4. Every time you rotate filters, add 5ml of Clearwater Blue copper ion and re-check copper ion levels
5. If you don't use the tub for 2 weeks, add about half an ounce of the lithium hypochlorite and mix per above.
6. Keep a surface scum filter inside your skimmer. I use Zorbo...and change it about every 8 weeks before they start breaking down
7. Keep your ozonator working...I upgraded mine to the next higher output. They don't last forever...if you stop seeing bubbles coming out of the jet attached to the ozonator (while the jets are on low, but no air being added), then replace your ozone module.

8. I have the tub set to filter for 8 hours per day...the maximum on our tub.

Since I've adopted this mix of methods (lithium chlorite, ozone, Blue), we've never had a cloudy, itchy or scummy hot tub...and our water lasts 2-3x longer.

I still check pH and alkalinity...pH is occasionally out of range and I adjust...but very rarely. I am concerned that my residual chlorine drops to nearly zero between tub uses, so I may start adding a half ounce of lithium chlorite more frequently to keep some free chlorine in the tub.

Feel free to sling arrows at my methods, as they may seem excessive, expensive or inappropriate...but I've finally got things settled down for our tub and the way we use it.

[chem geek]

This is a variation of the Dichlor-then-bleach method described on this site (and others) -- see Dichlor/bleach Method In A Nutshell. Bleach is far less expensive that lithium hypochlorite, but being a liquid it's easier to splash and bleach one's clothes.

As for insurance if the chlorine level gets too low, using Nature² with silver ions is another alternative to the copper ions of Clearwater Blue, though if the ozonator is strong enough and on frequently enough it can also keep the water in decent shape. Just note that ozone reacts with chlorine so is helpful if you use the spa every day or two as it reduces chlorine demand (by oxidizing some of the bather waste), but if you use the spa infrequently such as only on weekends then an ozonator can increase chlorine demand using up chlorine in between soaks.

[Tanakaba]

Good thoughts and thank you.

My ozonator is on all of the time...and it is an oxidizing beast. I bumped it up one size from OEM when I replaced it.

I also believe that monthly filter change outs and meticulous cleaning of bio-grunge from the valley of each pleat has really helped drop itchy skin events to zero. It's a 20 minute job to clean the entire filter by hand, and it's a bit rough on the fingers so I wear dishwashing gloves. It's satisfying to know that spotless filters are not re-contaminating the tub.

I have avoided bleach because of the splash issues, and the 5 lb bottle of granular lithium chlorite takes up much less space for six months of tub treatment. It is costing me about $45 for 6 months of LiCl, which I consider to be very reasonable. Also, bleach appears to have less available chlorine than LiCl (3%-10% versus 35%).

I wondered if lithium uptake via skin absorption would be an issue, but I found a research paper on the topic where blood serum levels of Li were measured in bathers in a LiCl tub and zero uptake was noted. I was hoping I could drop my psychiatrist's prescription...but no dice

I looked at the silver ion instead of copper ion...but I really don't want to go back MPS, which appears to be necessary to make the silver ion function as a strong sanitizer. If you have any other thoughts on how I might get the benefit of silver without the drag of MPS, please let me know. I resist MPS because it's another chemical that I have to own and concentration that I have to monitor.

Simple is elegant...and that's how we wish to keep things when out back soaking up the stars.

[chem geek]

Clorox regular unscented concentrated bleach is 8.25% and the rest is water and salt so the lower concentration only matters in terms of requiring more volume than the 35% Available Chlorine with lithium hypochlorite. But from a price point of view the bleach is 1/4th the price. Completely up to you, but the lower concentration of available chlorine just means you add more. The pricing comparison is PER FC, not per weight or volume so you are really paying more for the lithium hypochlorite, but as you point out it's compact and doesn't splash.

You most definitely want to start out using Dichlor initially to build up some CYA and you'll want to use Dichlor about one day per month to maintain the CYA since it gets slowly oxidized by chlorine (it might also somewhat from the hydroxyl radicals from ozone breakdown). If you don't have any or sufficient CYA in the water, then the active chlorine level will be too strong and harsh and will get used up too quickly (and outgas faster).

As for disinfection with copper and silver, they affect different bacteria. Copper isn't good with fecal bacteria while silver is. You can see a comparison of kill times with these and with chlorine (with CYA in the water) in this post.