About
About reefcalcs
reefcalcs is a free reference for reef and saltwater aquarium chemistry. Calculators that show their work, parameter guides that cite their sources, and zero up-sells.
Why this exists
The reef tank hobby has a primary-source problem. Most numbers that get repeated on forums trace back to a handful of articles by Randy Holmes-Farley, written in the early 2000s, that almost nobody reads anymore. The articles are still correct — they just got compressed into rules of thumb, then misquoted, then turned into product marketing, until the original chemistry was lost.
This site cites the source on every number. If a calculator says "1 mL of Part 2 per gallon raises alkalinity by 0.135 dKH," there's a link directly to Randy's Recipe 1 where that number comes from. If a parameter range says "target 8–9 dKH," there's a link to his optimal parameters thread.
If I can't cite it, I don't publish it. A few things on this site that other calculators include — pea gravel substrate density, certain "bowfront tank" volume formulas — are absent here because nobody publishes the source data. The methodology page documents what got cut and why.
Who built it
One person, ten years into the hobby, who got tired of doing two-part math in a notes app every Sunday morning. Not a chemist, not a marine biologist — just someone who reads the primary literature and writes calculators that don't lie about where their numbers come from.
What it costs
Nothing. No accounts, no email collection, no "upgrade to pro," no upsell to a salt brand. The site is static HTML — your browser does all the math locally. Aggregate page-view counts are kept via Vercel Analytics, which doesn't set cookies and doesn't track individuals.
If something is wrong, email hello@reefcalcs.com. The fastest way to a correction is to send the citation that contradicts what's here.
What it isn't
This site doesn't tell you which salt brand to buy, which LEDs are best, or what coral to put in your tank. It doesn't sell anything, doesn't take affiliate commissions, and doesn't carry advertising. If you want a forum, go to Reef2Reef. If you want product reviews, go to Bulk Reef Supply's videos. This site is the chemistry layer, and only the chemistry layer.
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