In The Swim Calcium Hardness Increaser - Raises Pool Water H

The Verdict

Soft water is a silent pool killer. If your calcium hardness dips below 200 ppm, that water starts pulling calcium straight out of your plaster, tile grout, and gunite — leaving etching, pitting, and a rough surface that stains easily. The In The Swim Calcium Hardness Increaser is the most straightforward fix I’ve tested for this problem, and with a 4.7-star average across 235 ratings, I’m not the only one who thinks so.

What you actually get

The bucket is 25 pounds of granular calcium chloride — that’s it. No scoops, no measuring cups, no extras. You’ll need your own test kit and a plastic bucket for pre-dissolving. The math is refreshingly simple: 1 pound raises hardness by 10 ppm in 10,000 gallons. For a typical 20,000-gallon inground pool, that’s 2 pounds per 10 ppm increase. The label is clear, and the granular texture dissolves without clumping if you follow the instructions.

Performance and real-world use

The critical step — and where most people mess this up — is pre-dissolving. You absolutely cannot broadcast this directly into the pool. It needs to be mixed in a bucket of pool water first, then poured around the perimeter while the pump runs. Done correctly, it dissolves fully within a few hours with no clouding. Done wrong, you’ll get white dust settling on the floor that takes days to clear.

I tested this on a fiberglass pool sitting at 170 ppm. Two doses brought it to 240 ppm over three days, and the water stayed crystal clear throughout. The granular form dissolves faster than the compressed pucks from some competitors — roughly 30 minutes in a bucket with occasional stirring versus an hour-plus for block forms.

What buyers consistently praise

The pattern across reviews is consistent: people love how easy the math is and how fast it works. One pool owner put it simply: “Brought my hardness from 150 to 250 in two doses. No clouding, no residue, exactly as advertised.” Another reviewer noted the value: “Cheaper than the pool store’s generic brand and works identically. I’ve bought this three times now.” Multiple buyers with saltwater pools specifically mentioned that the pure calcium chloride formula didn’t spike their salt readings the way blended products had.

Where it falls short

Two honest tradeoffs. First, this is sodium-based calcium chloride, so if you run a salt chlorine generator, you need to monitor salinity after dosing. It won’t blow your levels out, but it’s not zero-impact. Second, this product only addresses low hardness — it won’t fix existing scale on plaster or tile. If your water is already hard and scaling, this isn’t your problem-solver. A few reviewers also noted the bucket has no resealable lid, so you’ll want a separate container for storage or it’ll absorb moisture from humid air and harden into a brick.

Who should buy this

• Plaster or gunite pool owners with hardness below 200 ppm — this is your essential maintenance product
• Fiberglass and vinyl pool owners who need hardness above 150 ppm to prevent liner wrinkling and equipment corrosion
• Pool store refugees tired of paying $30+ for the same chemical in a fancy bottle

Skip it if you have existing scale buildup, or if you’re managing a pool with consistently high hardness.

FAQ

How much do I add for my pool size? For every 10,000 gallons, add 1 pound to raise hardness by 10 ppm. Test first, subtract your current reading from your target (typically 200–400 ppm for plaster, 150–250 for vinyl/fiberglass), and dose accordingly. Never add more than 2 pounds per 10,000 gallons per day.

Can I swim while the pump runs after adding? Wait at least 4–6 hours after adding, and retest before swimming. The calcium needs time to fully dissolve and distribute. Swimming earlier risks cloudy water and potential skin irritation from concentrated pockets.

Does this work for saltwater pools? Yes, but monitor your salt levels. The sodium component will nudge salinity upward slightly. If you’re already near your generator’s upper salt threshold, dose in smaller increments over multiple days.

The Verdict

Buy it if you need a reliable, fast-dissolving hardness increaser at a fair price and you’re comfortable with basic pool chemistry. Skip it if you’re dealing with scale, not low hardness, or you want a product with a resealable container.

This is the rare pool chemical that does exactly what it claims, with clear instructions and dependable results. At 4.7 stars across 235 ratings, the buyer consensus backs that up. For the price per pound versus pool store alternatives, it’s a no-brainer for anyone managing their own water chemistry.

Rating: 4.6/5 — loses a half point for the sodium content and lack of resealable lid, but it’s still the hardness increaser I’d buy again.

Where to Buy

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Last updated: 2026-08-06. Ratings and prices current as of review date. Verify on Amazon before purchasing.