Pool Opening Chemicals

Filter before you dose anything

A pool coming off a winter cover is not a chemistry problem yet. Water that has sat still for months is stratified, full of suspended debris, and completely unrepresentative at the surface where you are about to take a sample.

Get the equipment running, let the water turn over at least once, and skim and vacuum the obvious debris out. Only then test. Dosing a pool from a sample taken out of stagnant water means dosing for a pool that does not exist.

The sequence, and the one step people reverse

1. Circulate and filter. Run the pump continuously, backwash or clean the filter once the pressure climbs, and get the water moving before anything else.
2. Test. Alkalinity, pH, calcium hardness, cyanuric acid and chlorine. Winter changes all of them, and the dose tables on how to balance pool water all start from a number you measured.
3. Add a metal sequestrant. Every kit here includes one, called Metal Out or Stain Away. It binds dissolved iron and copper so they stay in solution.
4. Correct alkalinity, then pH. Alkalinity is the buffer, so it comes first - how to raise alkalinity and how to lower it cover both directions.
5. Shock. Now, after the sequestrant has had a few hours to work and with the pump running. Best pool shock covers which type to use.
6. Algaecide once chlorine drops back toward normal. High chlorine destroys most algaecides, so adding it with the shock wastes it.
7. Retest 24 hours later and again after a few days. Opening chemistry moves as the water warms.

What an opening kit actually contains

Kits bundle four or five products that are all bought separately anyway. The value is convenience and a sequence someone has already thought about - not a lower price per pound.

Two of these publish quantities and two publish a gallon rating. That is the difference between knowing what you bought and trusting the box - and it is why the value kit, which itemizes every bottle, is the easiest to judge even though it is the smallest.

Sizing the shock, not the kit

The weakest part of most kits is the shock quantity. One pound of dichlor is a single dose for a small pool, and an opening frequently needs more than a single dose because the water has a season of organic load in it.

If your pool is over roughly 15,000 gallons, buy the shock separately and treat the kit as the sequestrant, clarifier and algaecide bundle it really is.

Which kit for which pool

• Well water, or a history of spring stains. The In The Swim well-water kit is built around metal staining rather than treating it as a secondary feature.
• Salt pool. The In The Swim saltwater kit uses dichlor and a non-metallic algaecide, and states the largest volume here at 35,000 gallons. Copper-based algaecides and salt systems are a poor combination.
• Standard chlorine pool up to 30,000 gallons. Doheny's Ultimate is the only kit that publishes a gallon range and includes everything.
• Small pool on a budget. The In The Swim value kit itemizes every bottle and costs least, as long as you accept the 1 lb shock limit.
• A pool that was closed dirty. Add the enzyme bottle to whichever kit you buy - it targets the oily film shock burns itself out on.

What a kit will not do

No kit balances your water. Not one of them contains alkalinity increaser, pH adjuster or calcium hardness increaser, because those doses depend on readings nobody can guess from a box.

That is the honest limit of the format: a kit handles the seasonal jobs - sequester, shock, clarify, kill algae - and you still need the balancing chemicals and a test kit that reads more than chlorine and pH. A drop kit that measures alkalinity, hardness and cyanuric acid pays for itself in a single opening.

The picks

Top pick - One box that covers the whole opening

Doheny's Ultimate Pool Opening Start-Up Kit

The most complete opening kit here and the only one that states its gallon range. Metal Out first is the right sequence, and the kit is packed in that order.

The published figure

Listing states Metal Out, algae control, clarifier and Super Shock Plus, plus test strips; treats 10,000-30,000 gallons

Doheny's states the kit contains Metal Out (stain, rust and scale preventer), algae control, water clarifier and Premium Super Shock Plus, with a 10-pack of test strips included.

The stated treatment range is 10,000 to 30,000 gallons, and for larger pools the listing says to buy multiple kits. That is a real number to size against, which most kits do not give.

Metal sequestrant before shock is the part people get backwards. Shocking first oxidizes dissolved iron and copper and drops them onto the plaster as stains - see the metal remover page for the full argument.

What it does well

• States a treated volume range, 10,000-30,000 gallons
• Includes sequestrant, algaecide, clarifier and shock
• Test strips included, so you can check before dosing

What it costs you

• No individual product quantities published
• Shipped by a pool retailer, so delivery time varies
• One kit will not cover a 40,000 gallon pool

Skip it if your fill water is well water heavy in iron. The well-water kit is built for that instead.

$44.99 - View on Amazon

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Pick 2 - A pool filled from a well

In The Swim Well Water Pool Start-Up Kit

The opening kit for the pools that stain every spring. If your fill water comes from a well, this is the version to buy.

The published figure

Listing states shock, clarifier, algaecide, stain prevention, oil absorber and test strips, aimed at iron and mineral-heavy fill water

In The Swim states the kit is built for the problems well water causes at opening: iron, metals and mineral-heavy fill water, with a stain prevention treatment to reduce discoloration on liners, steps and surfaces.

The contents are stated as shock, clarifier, algaecide, stain prevention, oil absorber and test strips - the same shape as a standard kit with the sequestrant doing more of the work.

It is stated to suit both above-ground and inground pools.

What it does well

• Built around metal staining rather than treating it as an afterthought
• Includes an oil absorber, which most kits leave out
• Test strips included

What it costs you

• No treated-volume figure published
• No individual quantities stated
• Overkill if your fill water is municipal and soft

Skip it if you are on city water with no staining history. A standard kit costs less.

$36.97 - View on Amazon

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Pick 3 - The cheapest complete set of opening chemicals

In The Swim Basic Swimming Pool Chemical Value Kit

Every quantity published, at the lowest price of the kits here. The trade is that one pound of shock does not open a large pool.

The published figure

Listing states 1 qt Stain Away, 1 qt clarifier, 1 lb Di-Zap multi-shock, 1 qt algaecide, a Sun Sorb absorber and 4-way test strips

The listing itemizes the kit: 1 quart Stain Away, 1 quart clarifier, 1 lb Di-Zap multi-shock, 1 quart algaecide, one Sun Sorb oil absorber and a 10-count 4-way test strip pack.

One pound of dichlor is a single shock dose for a small pool. On anything above roughly 15,000 gallons, plan on buying shock separately - the shock page covers what to buy.

The listing notes the label may read 'Opening Kit' or 'Chemical Value Kit', which are the same product.

What it does well

• Every quantity published
• Cheapest complete kit on this page
• Includes sequestrant, clarifier, algaecide and strips

What it costs you

• Only 1 lb of shock, which is thin for a full opening
• No treated-volume figure published
• Label naming is inconsistent, per the listing

Skip it if your pool is over about 15,000 gallons. Buy shock separately or buy a larger kit.

$36.98 - View on Amazon

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Pick 4 - A salt pool, and the biggest stated volume here

In The Swim Saltwater Pool Opening Chemical Kit, up to 35,000 gallons

The only kit here that publishes its quantities. Four pounds of dichlor, a non-metallic algaecide and a sequestrant, sized for a big pool.

The published figure

Listing states four 1 lb bags of dichlor, non-metallic algaecide, clarifier, stain and scale preventer and Sun Sorb; up to 35,000 gallons

In The Swim states the contents precisely: four 1 lb bags of Di-Zap sodium dichlor, a non-metallic algaecide, a clarifier, a stain and scale preventer, and a Sun Sorb oil absorber.

Dichlor is the right shock for a salt pool at opening because it dissolves fast and is pH-neutral enough not to fight the chemistry you are about to set - though it adds cyanuric acid, which matters over a season.

The listing carries an unusually honest note: the packaging does not say 'salt water opening', but the treatments included are compatible with salt pools. That is the maker telling you what the box will look like when it arrives.

What it does well

• Publishes actual quantities, four 1 lb bags of dichlor
• Non-metallic algaecide, which suits a salt pool
• Rated up to 35,000 gallons

What it costs you

• Dichlor adds cyanuric acid with every dose
• The packaging does not match the product name, per the listing
• The most expensive kit on this page

Skip it if your pool is chlorine rather than salt, or under about 20,000 gallons. You are paying for volume you will not use.

$73.99 - View on Amazon

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Pick 5 - The winter scum line a shock will not touch

MAV AquaDoc Pool Opening Chemical, 16 oz enzyme

Not a kit - one bottle that does the job shock does badly. Enzymes break down the oily film a closed pool grows, instead of burning chlorine on it.

The published figure

Listing states a natural enzyme treatment for up to 15,000 gallons, compatible with cartridge, DE and sand filters and all sanitizers

AquaDoc states the product contains natural enzymes that break down non-living organic debris, and is sized for pools up to 15,000 gallons.

That is a genuinely different job from shocking. Chlorine will oxidize the oils and waterline film a covered pool accumulates over winter, but it spends a lot of itself doing it - which is why a pool can swallow shock at opening and still look dull.

It is stated to work with cartridge, DE and sand filters and with chlorine, bromine or saltwater sanitizing.

What it does well

• Targets the organic film rather than the chlorine demand
• Stated compatible with all three filter types and all sanitizers
• Cheapest single addition to an opening routine

What it costs you

• Not a kit - no shock, algaecide or sequestrant included
• Sized for 15,000 gallons per bottle
• Enzyme products publish no measurable result you can test for

Skip it if your pool was closed clean and covered tightly. There may be little organic film to break down.

$19.99 - View on Amazon

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Pick 6 - The reference residential kit

Taylor K-2006 Complete FAS-DPD Pool Test Kit

The kit every pool forum names, and for once the consensus is right - because titration is the one chlorine method that does not saturate exactly when you need it.

The published figure

FAS-DPD titration for free and combined chlorine, plus pH, acid and base demand, total alkalinity, calcium hardness and cyanuric acid; 3/4 oz reagents

The chlorine test is FAS-DPD: you add reagent drop by drop until a pink sample turns clear, and count the drops. Each drop is a fixed amount of chlorine, so 20 ppm reads as more drops rather than as an impossible shade of pink. Every color-match method tops out around 5 ppm - the range you are in during a shock.

The other six tests are the same reagents as the cheaper K-2005. What you pay extra for is the chlorine method and nothing else.

The 3/4 oz reagent bottles are what separate it from the K-2006C. They run out in a season of frequent testing on one pool; the C's 2 oz bottles do not.

What it does well

• Reads chlorine accurately at shock levels, which no strip can
• Covers all seven residential parameters
• Reagents are sold individually, so the case lasts for years

What it costs you

• 3/4 oz bottles empty quickly if you test more than weekly
• A full run takes minutes rather than seconds
• Several times the price of a strip bottle

Skip it if you never shock and test once a week. A strip kit gets used, and this one might not.

$86.12 - View on Amazon

$91.93 · 6% off

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Opening a green pool is a different job

If the cover comes off and the water is green rather than dull, stop treating this as an opening. A bloom needs a shock dose calculated for the algae, brushing, and filtration hours - the sequence is on how to clear a green pool fast.

The opening kit is still useful afterwards. Sequester the metals first, clear the algae, then use the clarifier and the algaecide as the preventative they are meant to be.