Calcium Hardness: Why It Matters
Adjusting calcium hardness vs leaving it alone: plaster etching, scale, heater damage, vinyl pools and when it genuinely matters.
The short version
Low calcium water is aggressive and will pull calcium from wherever it can find it, etching plaster and attacking heater components. High calcium scales surfaces and equipment. Vinyl and fibreglass pools tolerate low calcium better than plaster, which is why advice differs. Adjust it in plaster and heated pools; watch it in vinyl pools where the risk is scale rather than etching.
At a glance
| Clorox Pool Calcium Hardness Increaser | In The Swim Alkalinity Increaser | |
|---|---|---|
| Protects plaster | Yes | Indirectly |
| Protects a heater | Yes | Indirectly |
| Matters in vinyl pools | Less | Yes |
| Easy to lower | No, requires dilution | Yes |
| Typical target | 200 to 400 ppm plaster | 80 to 120 ppm |
| Adjust order | After alkalinity | First |
Choose the Clorox Pool Calcium Hardness Increaser if…
You have a plaster or pebble pool, or a heater. Aggressive low-calcium water etches plaster surfaces permanently and corrodes heat exchangers, and both repairs cost far more than the chemical.
Check Clorox Pool Calcium Hardness Increaser on Amazon
Choose the In The Swim Alkalinity Increaser if…
Balance is a sequence rather than a set of independent numbers. Alkalinity first, then pH, then calcium, because each affects the ones after it and adjusting out of order means doing it twice.
Check In The Swim Alkalinity Increaser on Amazon
Related
Comparison based on published manufacturer specifications and the general consensus of owner reports. We have not tested these products side by side. Confirm current specifications and prices before buying. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.
Frequently Asked Questions
How do I lower calcium hardness?
By diluting, which means draining part of the pool and refilling. There is no chemical that removes it, which is why it is worth not overshooting when adding.
Does a salt pool change this?
Salt itself does not affect calcium hardness, though salt pools tend to run high pH, which combined with high calcium encourages scale on the cell. Cell scaling is a common salt pool maintenance issue.
What is the Langelier index?
A calculation combining pH, alkalinity, calcium, temperature and dissolved solids to indicate whether water is scaling or corrosive. It is more useful than any single number in isolation.
Taking care of a pool?
Use our free calculators and guides to get every number right.
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