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Hot tub chemistry guides

Plain-English hot tub chemistry: chlorine, bromine, shock, pH, foam, cloudy water, inflatables and draining, with a calculator in every guide.

Sanitizer

Bromine vs Chlorine for Hot TubsBromine vs chlorine for hot tubs, honestly compared: how each works, cost, smell, skin feel, testing, inflatables, and why switching back needs a drain.

Problems and fixes

Cloudy Hot Tub Water: Causes and FixesWhy hot tub water turns cloudy (low sanitizer, high pH or alkalinity, dirty filter, old water, biofilm) and the order to fix it, including after a shock.
Hot Tub Foam: Causes and FixesWhat makes hot tub water foam (soaps, lotions, detergent, old water, low sanitizer, soft water) and how to fix it for good, not just with defoamer.

pH and alkalinity

Hot Tub pH Too High: Why It Rises and How to Lower ItWhy hot tub pH climbs (jets, high alkalinity, fresh fill water), how to lower pH and alkalinity with pH decreaser, and how borates keep it stable.

Shock

Hot Tub Shock: When, Which Type, and How Long to WaitChlorine shock vs non-chlorine (MPS) shock, how often to shock a hot tub, how much to use, and what to test before you get back in.

Volume

How Many Gallons in a Hot Tub?Typical hot tub volumes, how to calculate gallons or litres for square, round and inflatable tubs, and two ways to measure your tub's real volume.

Bromine

How Much Bromine to Add to a Hot TubHow to start a bromine hot tub with a bromide bank, how much tablets or granules to use, the right bromine level, and how to fix low or high readings.

Chlorine

How Much Chlorine to Add to a Hot TubChlorine amounts per 1 ppm for dichlor, liquid chlorine and bleach, plus the dichlor-then-bleach method, after-soak dosing and shock for any hot tub.

Draining

How Often Should You Drain a Hot Tub?The water replacement formula the spa industry uses, worked examples for acrylic and inflatable tubs, and the signs your water needs changing early.

Inflatable tubs

Inflatable Hot Tub Chemicals: The Complete GuideWhich chemicals an inflatable hot tub needs (Lay-Z-Spa, Intex PureSpa, SaluSpa, MSpa), how much for your volume, first-fill steps and a simple routine.