What Hot Tub Chemicals Do You Actually Need?

Walk into any pool store, tell them you just bought a hot tub, and walk out with a bag full of 10 to 12 different bottles. It happens every time. Half of those products are unnecessary for most owners, and a few of them are the exact same chemical sold under different names at different prices.

Here’s what you actually need, what’s situational, and what you can skip entirely.

The essentials (you need all of these)

Five products cover the core of hot tub water care. Everything else builds on top of them or doesn’t matter at all.

1. Sanitizer

Your sanitizer kills bacteria. Without it, warm water at 100 to 104 degrees becomes a breeding ground within hours. You have two good options.

Chlorine (dichlor granules): Sodium dichloro-s-triazinetrione, sold as “chlorinating granules” or “chlorinating concentrate.” Dissolves in minutes, has a near neutral pH (6.5 to 7.0), and is easy to dose in small amounts. Target free chlorine of 3 to 5 ppm. Maintenance dose is about 1/4 to 1/2 teaspoon per 100 gallons.

Never use trichlor (trichloroisocyanuric acid). Those are pool tablets with a pH of 2.8 that destroy hot tub equipment and overwhelm small water volumes with cyanuric acid. Read the label before you buy. If it says trichlor, put it back.

Bromine (BCDMH tablets): Bromo-chloro-dimethylhydantoin (BCDMH) tablets go in a floating dispenser. Target 3 to 5 ppm bromine. Bromine stays more stable at hot tub temperatures, works across a wider pH range, and produces less odor than chlorine. The trade-off is that it costs more per month and requires a floating feeder. For a full comparison, see bromine vs chlorine.

Pick one system. Don’t mix them.

2. pH decreaser

Sodium bisulfate, sold as “pH decreaser,” “pH minus,” or “dry acid.” Hot tubs drift alkaline because hot water loses CO2 faster, which pushes pH up. You’ll use this more than any other balancing chemical.

About 1 tablespoon per 200 gallons lowers pH by roughly 0.2 points. The target is 7.4 to 7.6. Small doses, test, adjust. Don’t dump and hope.

3. Alkalinity increaser

Sodium bicarbonate. That’s baking soda. The pool store sells the identical chemical in a fancier container for several times the price. A box from the grocery store works the same way.

Target total alkalinity of 80 to 120 ppm. About 1 tablespoon per 100 gallons raises alkalinity by roughly 10 ppm. Always adjust alkalinity before pH, because alkalinity acts as a buffer that determines how stable pH stays.

4. Shock oxidizer

Shocking breaks down organic waste (body oils, sweat, lotions, dead skin cells) that accumulates even when sanitizer levels look fine. You want two types on hand.

Non-chlorine shock (MPS): Potassium monopersulfate. Oxidizes waste without adding chlorine or cyanuric acid. You can soak 15 to 20 minutes after adding it. Great for weekly maintenance. About 1 ounce per 250 gallons.

Chlorine shock: Just a higher dose of your regular dichlor (or bleach). Kills bacteria AND oxidizes waste. Use after heavy use, parties, or when the water smells off. Target 10 ppm free chlorine, then wait 4 to 8 hours before soaking.

5. Test strips (or a liquid test kit)

You can’t dose what you can’t measure. A 4-way test strip that reads free chlorine (or bromine), pH, total alkalinity, and calcium hardness covers your weekly needs.

For more precision, the Taylor K-2006 liquid test kit is the gold standard. It uses FAS-DPD chemistry, which avoids the false chlorine readings that MPS causes on regular test strips.

Test two to three times per week. Before you add anything, test. After you add something, wait 20 minutes, test again.

The chlorine routine vs the bromine routine

Both systems need the same balancing chemicals (pH decreaser, alkalinity increaser, shock, test kit). The difference is the sanitizer and a couple of extras.

Chlorine setup: dichlor granules + everything above. Optional: plain unscented bleach once you switch to the dichlor/bleach method.

Bromine setup: bromine tablets + floating dispenser + sodium bromide (to establish the bromide bank at startup) + everything above.

Bromine requires the dispenser and the initial sodium bromide dose that chlorine doesn’t. Beyond that, the routines are nearly identical.

Situationally needed (buy only if your water requires it)

These aren’t for everyone. Whether you need them depends on your fill water, your tub’s age, and how you use it.

Calcium hardness increaser. Calcium chloride. Only needed if your fill water tests below 150 ppm. Many municipal water supplies already have adequate calcium. Test your tap water before buying. If it’s in the 150 to 250 ppm range, you don’t need this at all. One correction at fill time lasts the entire water cycle since calcium doesn’t drift much on its own.

Pipe flush (biofilm remover). Products like Ahh-Some or Oh Yuk strip biofilm from your plumbing lines. Use it before every drain and refill (every 3 to 4 months) and before the very first fill on a brand new tub. Factory test water and residue sit in those pipes for months. Flushing before your first fill prevents weeks of unexplained chemistry problems. Not a monthly purchase, more like twice a year.

A hose pre-filter makes sense if your tap water tests above 250 ppm calcium, if you’re on well water with metals (iron, manganese), or if you see staining right after filling. It strips those minerals before the water hits the tub. One cartridge lasts one or two fills.

Sequestering agent (stain and scale preventer). Only needed if you’re on well water with dissolved metals. Add it before your first chlorine dose after filling, because chlorine oxidizes dissolved iron and copper into visible particles that stain the shell. If your tap water is clear and comes from a municipal supply, skip it entirely.

pH increaser. Sodium carbonate (soda ash). Most hot tubs drift pH upward, so you’ll rarely need to raise it. If your fill water happens to come out below pH 7.2, a small dose brings it up. But honestly, just aerating the water (running jets with the cover off) raises pH without adding anything. Buy it only if you actually test low.

What you can skip

Here’s where the pool store and reality part ways.

Clarifier. A flocculant that clumps particles so the filter can catch them. Sounds useful. In practice, if your sanitizer is at 3 to 5 ppm, your pH is at 7.4 to 7.6, and your filter is clean, the water will be clear without it. Cloudiness almost always means a chemistry or filtration problem. Clarifier hides the symptom instead of fixing the cause.

Foam reducers are another common purchase that misses the point. Foam comes from body oils, laundry detergent residue on swimsuits, lotions, and dissolved organic waste. Defoamer knocks it down temporarily but the foam comes right back because the contamination is still there. The actual fix: shower before soaking, rinse swimsuits without detergent, and drain on schedule.

Aromatherapy crystals and spa fragrances. Zero water quality benefit. Some leave oily residue that clogs filters and creates scum lines. If you want them for the experience, that’s a personal choice, but it’s not maintenance.

Phosphate removers are one of the biggest pool store upsells. Phosphates feed algae in pools, but hot tubs at 3 to 5 ppm chlorine don’t grow algae. The sanitizer kills it before phosphates become relevant. Buying phosphate remover for a hot tub is solving a problem that doesn’t exist.

Algaecide. Hot tubs don’t grow algae when the sanitizer is in range. If you see green water, it’s either dissolved copper being oxidized by chlorine or a complete sanitizer failure. Neither one is fixed by algaecide.

“All-in-one” or “complete care” products. These try to sanitize, clarify, and prevent scale in one bottle. They do none of those jobs well. You can’t fine-tune individual parameters when everything is bundled. Skip them.

Mineral cartridges as a standalone system. Products like Nature2 or FROG @ease use silver and copper to supplement sanitation. They reduce chlorine demand but they don’t eliminate the need for a chemical sanitizer. Marketing that implies otherwise is misleading. If you use one, you still need chlorine or bromine.

The minimum viable kit

If you’re starting from scratch with a chlorine system and your tap water has reasonable chemistry (calcium 150 to 250 ppm, pH not wildly high), here’s the shortest possible shopping list:

1. Dichlor granules (2 lb container)
2. Sodium bisulfate / pH decreaser (2 lb container)
3. Baking soda (from the grocery store)
4. MPS non-chlorine shock (2 lb container)
5. Test strips (50 count bottle)

Five products. That’s it. If you plan to switch to the dichlor/bleach method after the first couple of weeks (recommended), add a jug of plain unscented bleach from the grocery store.

Everything else on the shelf can wait until you’ve tested your fill water and know what your tub actually needs. Don’t buy calcium hardness increaser until you’ve confirmed your water is below 150 ppm. Don’t buy a sequestering agent unless you have metals in your water. Don’t buy a pipe flush until your first drain day (though getting one early for a new tub is smart).

The experienced hot tub community has a saying worth remembering: the fewer products in your cabinet, the better your water probably looks.

Frequently asked questions

What chemicals do I need for a new hot tub? Five things: a sanitizer (dichlor granules or bromine tablets), pH decreaser (sodium bisulfate), alkalinity increaser (sodium bicarbonate, which is baking soda), shock oxidizer (MPS for routine use, dichlor for heavy situations), and test strips. Everything else is either situational or unnecessary.

Can I use baking soda in my hot tub? Yes. Baking soda is sodium bicarbonate, the same active ingredient sold as “alkalinity increaser” at pool stores. It raises total alkalinity without much effect on pH. Use about 1 tablespoon per 100 gallons to raise alkalinity by roughly 10 ppm.

Do I need clarifier for my hot tub? Almost never. Clarifier clumps tiny particles so the filter can catch them, but if your sanitizer and pH are correct and your filter is clean, the water should be clear on its own. Cloudiness usually means a chemistry problem that clarifier won’t solve. Fix the root cause instead.

What is the cheapest way to sanitize a hot tub? The dichlor then bleach method. Use dichlor granules for the first week or two after filling to build cyanuric acid to 30 ppm, then switch to plain unscented household bleach for all ongoing dosing. Bleach is widely available and adds zero cyanuric acid, so your chlorine stays fully active for the entire fill cycle.

Do I need different chemicals for a bromine hot tub? The balancing chemicals are the same: pH decreaser, alkalinity increaser, and shock. The difference is the sanitizer. Bromine uses tablets in a floating dispenser instead of granules, and you’ll need sodium bromide to establish a bromide bank at startup. Everything else overlaps.

Is a hot tub starter kit worth buying? Most starter kits include 8 to 12 products when you only need 5. They pad the box with clarifiers, foam reducers, aromatherapy crystals, and other products that aren’t necessary for basic water care. You’re better off buying the essentials individually and adding situational products only after you’ve tested your fill water.