HTH Frequently Asked Questions

HTH™ alkalinity increaser raises total alkalinity in pool water to the ideal range of 80–120 ppm, helping stabilize pH so it stops fluctuating. Balanced alkalinity protects pool surfaces, equipment, and swimmers from the effects of corrosive water.

Add HTH™ alkalinity increaser when your total alkalinity tests below 80 ppm. Low alkalinity causes pH to fluctuate erratically, which can lead to chlorine loss, skin irritation, and damage to pool surfaces and equipment.

Unstable pH is almost always caused by low total alkalinity. Alkalinity acts as a buffer that holds pH steady — when it is too low, even small amounts of rain, swimmers, or chemicals can push pH up or down quickly. Raise alkalinity first, then adjust pH.

The ideal total alkalinity range is 80–120 ppm for most pools. Staying within this range helps keep pH stable, allows chlorine to work efficiently, and helps prevent corrosion or scaling on pool surfaces.

With the pump running, add the recommended amount of HTH™ pool alkalinity increaser directly into the pool. Retest after 6–8 hours of circulation and repeat if needed until alkalinity reaches 80–120 ppm.

Yes. HTH™ Alkalinity Increaser is compatible with all pool types including saltwater, vinyl-liner, and concrete pools. Salt chlorine generators still require balanced alkalinity to function properly.

Low alkalinity (below 80 ppm) leads to rapid pH swings, corrosion of metal equipment and pool surfaces, eye and skin irritation, and faster chlorine consumption. Test and correct alkalinity before adjusting pH or adding other chemicals.

High alkalinity (above 120 ppm) can cause pH to rise and resist correction, leading to cloudy water, scaling on surfaces and equipment, and reduced chlorine efficiency. If alkalinity is above 120 ppm, use HTH™ pool pH Decreaser to bring it back into range.

HTH™ Calcium Hardness Increaser raises calcium levels in pool water to the recommended range of 200–400 ppm. Proper calcium hardness prevents water from becoming corrosive, which can etch plaster, and wear down equipment.

When calcium hardness drops below 200 ppm, 'soft' water aggressively pulls calcium from pool plaster, causing etching, pitting, and damage over time.

Most pools should maintain calcium hardness between 200–400 ppm. Plaster or concrete pools perform best at the higher end (250–350 ppm), while vinyl and fiberglass pools can be maintained toward the lower end of the range.

Slowly, add the recommended amout of HTH™ pool calcium hardness increaser directly into the pool with the pump running. Allow 48 hours of circulation before retesting. Never add more than 10 lbs per 10,000 gallons at one time.

Yes. HTH™ Calcium Hardness Increaser is safe for all pool types including vinyl-liner, fiberglass, and saltwater pools. Maintaining proper calcium levels protects every pool type from the effects of corrosive, unbalanced water.

Use HTH™'s 6-Way Test Kit or 6-Way Test Strips to measure calcium hardness. Test your pool water at least once a month, or more frequently at the start of the season or after significant water addition.

HTH™ Chlorine Stabilizer contains cyanuric acid (CYA), which acts like sunscreen for chlorine. Without it, UV rays from sunlight can destroy up to 90% of your pool's free chlorine within two hours, making it nearly impossible to maintain safe sanitizer levels.

For outdoor pools using trichlor or dichlor tablets, maintain CYA between 30–50 ppm. Salt chlorine generator pools typically need 60–80 ppm. Levels above 100 ppm can reduce chlorine effectiveness and are lowered by partially draining the pool.

Rapid chlorine loss in outdoor pools is almost always caused by low stabilizer (CYA) levels. Without enough CYA, direct sunlight destroys chlorine within hours. Test stabilizer levels and add HTH™ Chlorine Stabilizer if CYA is below 30 ppm.

Always check the back of HTH™ Pool Care Chlorine Stabilizer to determine the right dosage for your pool and use hthpools.com/pages/pool-calculator. Add the calculated dose directly through the skimmer with the pump running. CYA dissolves slowly — run the pump for 24–48 hours before retesting levels.

Cyanuric acid is mildly acidic and may slightly lower pH and alkalinity when added in large doses. Always retest pH and alkalinity after adding stabilizer and make any necessary adjustments.

High CYA (above 100 ppm) reduces the effectiveness of chlorine — a condition sometimes called 'chlorine lock' — meaning the pool requires much more chlorine to stay sanitary. The only reliable way to lower CYA is to partially drain and refill the pool.

HTH™ pH Increaser raises low pH back into the ideal range of 7.2–7.6. Low pH makes pool water acidic, which can corrode metal equipment, damage surfaces, irritate swimmers' eyes and skin, and cause chlorine to burn off faster.

The ideal pool pH range is 7.2–7.6. At this level, chlorine works most efficiently, water is comfortable for swimmers, and pool surfaces and equipment are protected from corrosion.

Pool pH can drop due to heavy rainfall, acidic fill water, high bather load, CO2 dissolved from the air, or the addition of certain chemicals like shock or chlorine products. If alkalinity is also low, pH will be especially difficult to stabilize.

With the pump running, add the recommended amount directly into the pool. Run the pump for 4–6 hours before retesting. Adjust in small increments to avoid overshooting the target range (7.2-7.6).

HTH™ pH increaser starts dissolving and acting within minutes of being added. You should retest after 4–6 hours of pump circulation to get an accurate reading and determine if a second dose is needed.

No — add one chemical at a time and wait at least 4–6 hours between additions. Adding pH increaser and chlorine simultaneously can cause localized reactions and makes it impossible to accurately assess the effect of each adjustment. Always adjust pH and alkalinity first, allow them to circulate fully, then add sanitizer last.

HTH™ pH Decreaser lowers high pH back into the safe range of 7.2–7.6. High pH reduces chlorine effectiveness, can cause cloudy water, scaling on surfaces and equipment, and eye irritation for swimmers.

Pool pH commonly rises due to the addition of alkalinity or calcium chemicals, high-pH fill water, saltwater systems, algae growth, or heavy aeration from waterfalls or fountains. If alkalinity is also high, it will push pH up consistently.

With the pump running, broadcast the recommended dose of HTH™ pH decreaser around the deep end of the pool. Never pre-dissolve pH down in a plastic bucket — add it directly to pool water. Retest after 4–6 hours of circulation and adjust if necessary.

High pH (above 7.8) significantly reduces chlorine efficiency, meaning bacteria and algae can survive even with adequate chlorine levels present. It also causes calcium scaling on pool walls, filters, and equipment.

Yes. pH Decreaser (sodium bisulfate or muriatic acid) lowers both pH and total alkalinity. If alkalinity is already in range, use smaller doses and retest frequently to avoid dropping alkalinity below 80 ppm.

Wait at least 4–6 hours after shocking before adding HTH™ pH Decreaser, and vice versa. Adding acid immediately after a high-chlorine shock can cause off-gassing and interfere with both treatments. Always test pH after a shock treatment has distributed fully before making any pH adjustment.

The HTH™ 6-Way Test Kit tests for free chlorine, total chlorine, bromine, pH, total alkalinity, calcium hardness, and cyanuric acid (stabilizer). These are the six most important parameters for maintaining safe, clear, and balanced pool water.

Test your pool water at least 2–3 times per week during swim season. Test more frequently after heavy rain, a large number of swimmers, adding chemicals, or at pool opening and closing. Regular testing prevents problems before they become costly.

Target these ranges: Free Chlorine 1–4 ppm, pH 7.2–7.6, Total Alkalinity 80–120 ppm, Calcium Hardness 200–400 ppm, and Cyanuric Acid 30–50 ppm. Keeping all parameters in range ensures sanitizer effectiveness and swimmer comfort.

Fill the test vial to the indicated line with pool water, add the appropriate reagent drops for each test, cap and invert to mix, then compare the color to the chart on the kit. Test away from direct sunlight for the most accurate color reading.

Yes, this test kit is compatible with both chlorine-based and saltwater pools. Note that it does not test salt (NaCl) concentration — use a dedicated salt test strip or meter if you need to verify salt levels in a saltwater pool.

Compare your results to the ideal ranges. If chlorine is low, add sanitizer or shock. If pH is off, add pH Up or pH Down. For low alkalinity, add Alkalinity Increaser. For low calcium hardness, add Calcium Hardness Increaser. For low CYA, add Chlorine Stabilizer.

HTH™ Pool Care pH Up

HTH™ Pool Care pH Down

HTH™ Pool Care Chlorine Stabilizer

HTH™ Pool Care Shock Advanced

HTH™ Pool Care Alkalinity Up

HTH™ Pool Care Calcium Up

Always adjust chemicals one at a time, starting with alkalinity, then pH, then calcium hardness, then chlorine/stabilizer. Wait 4–6 hours between adjustments and retest before adding the next chemical to avoid overcorrecting.

HTH™ 6?Way Test Strips measure free chlorine, bromine, pH, total alkalinity, calcium hardness, and cyanuric acid (CYA) — the six key parameters needed to maintain balanced, safe pool water.

For added convenience, users can scan their results with the HTH™ Test to Swim app, which analyzes the strip and recommends the exact HTH™ products and dosages needed.

Dip one strip into pool water at elbow depth for 2 seconds, remove without shaking, and hold flat (do not wipe). After 30 seconds, compare the color pads to the chart on the bottle in natural light. Record results and adjust chemicals as needed.

For instant digital results, users can download the HTH™ Test to Swim app and scan the test strip with their phone, or reference the online HTH™ pool test strip color chart at https://HTH™pools.com/pages/pool-test-strip-color-chart

HTH™ test strips provide fast, reliable readings suitable for routine pool maintenance and daily monitoring. When used with the HTH™ Test to Swim app, results are digitized and translated into clear treatment recommendations.

For the most precise measurements — especially at pool opening, closing, or when troubleshooting a problem — the HTH™ 6?Way Liquid Test Kit offers greater accuracy.

After dipping the strip for 2 seconds and waiting 30 seconds, compare each color pad to the matching row on the bottle chart in natural light. Retest if results seem unexpected, as sunscreen, lotions, or cross?contamination can affect readings.

Alternatively, scanning the strip with the HTH™ Test to Swim app eliminates guesswork and automatically interprets the results for you.

Low chlorine readings after dosing can indicate that CYA (stabilizer) is too low, sunlight is consuming chlorine rapidly, the pool has high chlorine demand from algae or organic load, or the strip has expired.

Use the HTH™ Test to Swim app to confirm stabilizer levels and receive specific dosing instructions. Always check the strip expiration date printed on the bottle.

Keep the bottle tightly capped at all times — even brief exposure to humidity degrades the reagent pads. Store in a cool, dry location away from heat, sunlight, and moisture. Never store in a bathroom, near the pool, or in a hot car.

Check the expiration date printed on the bottom of the bottle. When stored correctly, strips typically last 12–18 months after opening.

HTH™ 1-inch chlorine tablets are designed for smaller pools and above-ground pools. They dissolve slowly to maintain a steady chlorine level of 1–4 ppm, continuously killing bacteria and preventing algae.

A general starting point is 1–2 tablets per 5,000 gallons of water per week. Always test chlorine levels after a few days and adjust the number of tablets in your feeder or floater to maintain 1–4 ppm.

Always place chlorine tablets in a floating chlorine dispenser, an automatic chemical feeder, or a skimmer basket — never directly on the pool floor or walls. Direct contact with surfaces can cause bleaching or damage to liners and finishes.

1-inch tablets are sized for smaller pools, feeders designed for 1-inch tabs, and above-ground pools. 3-inch tablets dissolve more slowly and are ideal for larger in-ground pools. Use the size that matches your feeder type and pool volume.

Each 1-inch tablet typically lasts 5–7 days, depending on water temperature, sunlight exposure, pool size, and bather load. Higher temperatures and heavy use will cause tablets to dissolve faster.

No. Trichlor tablets — including 1-inch and 3-inch — should not be used in hot tubs. Their highly acidic pH (~2.8) damages acrylic shells, degrades rubber seals, and rapidly builds up CYA in the small water volume of a spa. For hot tub sanitation, use HTH spa™ Bromine Tablets, HTH spa™ Clear Chlorinating Sanitizer, or other products specifically formulated and labeled for spa use.

HTH™ 3-inch chlorine tablets provide long-lasting sanitation for in-ground and larger pools. Each tablet dissolves slowly over 5–7 days to continuously kill bacteria and prevent algae while maintaining chlorine levels of 1–4 ppm.

Start with 1 tablet per 10,000 gallons of water per week. Adjust up or down based on test results — your goal is to maintain a free chlorine level of 1–4 ppm. Hot weather, heavy use, and high bather loads may require additional tablets.

Low chlorine despite using tablets often means your CYA (stabilizer) is too low and sunlight is destroying chlorine, the pool has a heavy organic load requiring a shock treatment, or your feeder rate needs to be increased. Test all parameters and shock the pool if needed.

Yes. Standard HTH™ 3-inch Chlorine Tablets use trichlor (trichloroisocyanuric acid), which contains approximately 57% cyanuric acid by weight. This means CYA gradually accumulates in your pool as you use them. Test CYA monthly — when it reaches 50 ppm, consider switching to HTH™ Brilliance Cal Hypo Tablets (no CYA) to avoid over-stabilization.

Yes, when used correctly. Never place HTH™ 3" chlorine tablets tablets directly on a vinyl liner — always use a floater or automatic feeder. Trichlor tablets have a very low pH (~2.8) and can bleach or damage vinyl if concentrated contact is prolonged. A floating dispenser distributes chlorine safely throughout the pool without localized surface exposure.

Typically, is it not safe to break chlorine tablets. A better approach for smaller pools is to use HTH™ 1-inch chlorine tablets, which are specifically sized for smaller volumes and allow more precise dosing.

HTH™ 3-inch Advanced Tablets combine a slow-release chlorine sanitizer with a built-in clarifier and algaecide. This all-in-one formula helps keep water clearer and prevents algae growth without requiring as many separate product additions compared to standard chlorine tablets.

HTH™ Advanced Tablets supplement the use of algaecide and clarifier during normal maintenance. This will minimize the chance for algae growth and/or cloudy water.

If your pool was already out of balance when you switched to advanced tablets, the tablets alone may not be able to correct an existing problem — they are designed for maintenance, not remediation. Shock the pool, verify all chemical levels are in range, then resume tablet use.

Yes. HTH™ 3-inch Advanced Tablets use trichlor and contain CYA, just like standard 3-inch tablets. CYA will accumulate over the season with regular use. Test CYA monthly — when it approaches 50 ppm, consider switching to HTH™ Brilliance Cal Hypo Tablets for ongoing sanitation without adding more stabilizer. The clarifier and algaecide in Advanced tabs are not affected by switching to cal hypo.

HTH™ 3-inch Advanced Tablets contain a built-in water clarifier that helps coagulate fine suspended particles as the tablet dissolves. Rather than waiting for cloudiness to develop and then adding a separate clarifier treatment, the continuous low-dose clarifier in Advanced Tablets works proactively — keeping water clearer between weekly maintenance steps.

Yes. The built-in algaecide in HTH™ 3" Advanced Chlorine Tablets makes them a smarter choice for pools prone to algae — especially during hot weather or in pools where phosphate levels run high. The continuous low-level algaecide acts as a preventive barrier, making it harder for algae spores to take hold between shock treatments.