Best reef salt: match alkalinity to your tank

Every reef salt makes saltwater, but they don't all mix to the same chemistry. The number that matters most is mixed alkalinity — the dKH the batch lands at straight out of the bucket — because it has to fit how you run your tank. Buy the wrong alkalinity and every water change fights your dosing instead of helping it.

The ReefRig Alkalinity Match

Match the salt's mixed alkalinity to your husbandry style, not to a brand ranking:

• SPS, holding alkalinity high (~11–12 dKH): use a high-alk salt so water changes don't drag alkalinity down.
• Low-nutrient / ULNS SPS, or mixed reef run at natural levels (~7–9 dKH): use a low-to-moderate-alk salt so a water change doesn't spike alkalinity and burn tissue.
• Fish-only / FOWLR: alkalinity barely matters — buy on price.

Compare: five reef salts

Cost per gallon is at the mainstream package size. All prices verified July 2026.

Cheapest per gallon: Reef Crystals ($0.40), Fritz RPM ($0.42), Instant Ocean ($0.45). Alkalinity figures are typical mixed values, not lab-exact — always test your own batch.

Picks by tank type

• Fish-only / FOWLR: Instant Ocean Sea Salt ($0.45/gal). It mixes near natural-seawater alkalinity (~8 dKH) with no boosted calcium or magnesium you don't need. The cheapest reliable way to make saltwater.
• Beginner mixed reef: Instant Ocean Reef Crystals ($0.40/gal) or Fritz RPM ($0.42/gal). Reef Crystals mixes higher (~12 dKH) with boosted calcium, magnesium and trace elements; Fritz RPM runs moderate (~8.5 dKH) and is the easiest to keep stable.
• SPS growth tanks: Red Sea Coral Pro (~12 dKH). Elevated alkalinity, calcium and magnesium for fast stony-coral growth — ideal when you dose to hold parameters high.
• Low-nutrient / ULNS SPS: Tropic Marin Pro Reef (~7 dKH). Its low natural-seawater alkalinity is favored by keepers running lean systems who don't want water changes spiking alkalinity.

Packaging change to know about

Tropic Marin's 200-gallon bucket is discontinued — the salt now ships in boxes (100-gallon and 160-gallon). If you find an old 200-gallon bucket listing, that's the retired format; the salt itself is current and in stock in box form. Buy the box, not a stale bucket listing.

Bottom line

There is no single "best" salt — there's the salt whose mixed alkalinity fits your husbandry. Fish-only tanks buy on price (Instant Ocean), mixed reefs want moderate alkalinity (Fritz RPM / Reef Crystals), SPS growth tanks want it high (Red Sea Coral Pro), and lean SPS systems want it low (Tropic Marin). Size a water change or a fresh mix with the salt mix calculator, confirm the batch with the salinity conversion tool, and build the rest of your system in the System Builder.

Mixed-alkalinity values, package sizes and prices verified July 2026 (Bulk Reef Supply, SaltwaterAquarium.com, manufacturer sites). Alkalinity is a typical mixed figure, not a per-batch guarantee — test every batch before use. Re-check pricing before purchase.

Frequently asked questions

Which reef salt is best?

There is no single best salt — there is the one whose mixed alkalinity fits how you run your tank. Match it to your husbandry: Red Sea Coral Pro (~12 dKH) for SPS growth, Tropic Marin Pro Reef (~7 dKH) or Fritz RPM (~8.5 dKH) for low-nutrient or mixed tanks, and Instant Ocean for fish-only.

Why does the salt's alkalinity matter?

Because every water change swings your tank toward the salt's mixed alkalinity. Buy the wrong level and each change fights your dosing instead of helping — a high-alk salt keeps SPS tanks from dragging down, while a low-to-moderate salt keeps a change from spiking alkalinity and burning tissue on a lean system.

What's the cheapest salt for a fish-only tank?

Instant Ocean Sea Salt at about $0.45 a gallon — it mixes near natural-seawater alkalinity (~8 dKH) with no boosted calcium or magnesium a fish-only tank doesn't need. Reef Crystals ($0.40/gal) and Fritz RPM ($0.42/gal) are the other low-cost options.

What salt should a beginner mixed reef use?

A moderate-alkalinity salt is easiest to keep stable: Fritz RPM (~8.5 dKH, $0.42/gal) or Instant Ocean Reef Crystals (~12 dKH, $0.40/gal) with boosted calcium, magnesium and trace elements. The point is a salt whose water changes don't swing alkalinity several points overnight.

Is the Tropic Marin bucket discontinued?

The 200-gallon bucket is — Tropic Marin Pro Reef now ships in 100- and 160-gallon boxes. The salt itself is unchanged and in stock; just don't order from a stale 200-gallon bucket listing.