Privacy Policy

The short version

The calculators on reefcalcs run in your browser — your calculator inputs are not sent to us. You can use the entire calculator library without an account. If you choose to create an account, we store your email, a hash of your password, and the tank data you choose to save, so it syncs across your devices. We do not sell your data. We use aggregate analytics to understand which pages get visited. The site may include affiliate links and third-party ads, which are governed by their own privacy policies and disclosed below.

Calculations run in your browser

Every calculator on reefcalcs is a client-side JavaScript function. Your tank dimensions, dosing inputs, water parameters, and results are computed locally in your browser and are not transmitted to our servers as part of running a calculation. The only tank data that reaches our server is what you explicitly save to an account (see below).

What we store when you create an account

Accounts are optional. If you create one, we store the following in our database (hosted on Neon):

• Your email address — used to sign in, verify your account, send password resets, and (if you opt in) a weekly digest.
• A hash of your password — never the plaintext password. Passwords are hashed with bcrypt before storage; we cannot read or recover your original password.
• Your username — optional, only used if you choose to make a tank public.
• Tank data you choose to save — name, dimensions, target parameters, dosing schedule, and equipment list.
• Parameter logs — the test readings you record for a saved tank.

You can change your password and email-digest preference from your account page at any time. Transactional emails (verification, password reset, welcome) are sent via Resend.

Analytics

We use Vercel Analytics to record anonymized aggregate page views. It records the page URL, referring URL, country (derived from IP at request time, then discarded), device type, and browser/OS family. Vercel Analytics does not use cookies and does not store your IP address. See Vercel's analytics privacy policy for the full technical detail.

We may add additional analytics providers (e.g. Google Analytics) in the future. If we do, this policy will be updated and the date at the top of the page will move.

Affiliate links

Some outbound links on reefcalcs may be affiliate links — most commonly via the Amazon Associates program. If you click an affiliate link and make a purchase, reefcalcs may earn a commission at no additional cost to you. Affiliate links never change what a calculator outputs, what a parameter range is, or which product a comparison page recommends. The math and the cited sources come first.

As an Amazon Associate, reefcalcs may earn from qualifying purchases.

Third-party advertising (Google AdSense)

reefcalcs uses Google AdSense to display advertising. Google and its advertising partners may set cookies, use device identifiers (including the advertising ID on mobile devices), and collect information about your visits to this site and other sites in order to provide advertisements about goods and services that may interest you. This activity is governed by Google's privacy policy, not ours.

Specifically:

• Third-party vendors, including Google, use cookies to serve ads based on your prior visits to this website or other websites.
• Google's use of advertising cookies enables it and its partners to serve ads to you based on your visit to reefcalcs and/or other sites on the internet.
• You can opt out of personalized advertising by visiting Google Ads Settings. You can also opt out of a third-party vendor's use of cookies for personalized advertising by visiting aboutads.info.
• For more on how Google uses information from sites or apps that use its services, see policies.google.com/technologies/partner-sites and policies.google.com/technologies/ads.

Cookies and similar technologies

reefcalcs does not set first-party tracking cookies. The one first-party cookie we set is a strictly-necessary session cookie, and only after you sign in: it is an HTTP-only, secure cookie that keeps you logged in. It is not used for advertising or cross-site tracking. If you never create an account, we set no first-party cookies.

Third parties may set cookies through this site:

• Google AdSense may set advertising cookies (including the DoubleClick IDE and ANID cookies) to measure and serve ads.
• Google Analytics 4 (GA4) sets the _ga and _ga_<measurement_id> cookies to count unique visitors and measure how pages are used. IP addresses are anonymised before storage. We use the data to see which calculators are popular and which pages need improvement — not to profile individual users.
• Amazon may set cookies when you click an affiliate link and arrive on amazon.com.

Most browsers let you block or delete cookies in their settings. Blocking advertising cookies will not break the calculators on this site; it will only result in less relevant ads being shown to you.

Visitors from the EEA, UK, and Switzerland

If you are visiting from the European Economic Area, the United Kingdom, or Switzerland, you will see a consent banner on your first visit. The banner is provided by Google's certified Consent Management Platform (CMP) and complies with the IAB Europe Transparency & Consent Framework (TCF) v2 and the EU's Digital Markets Act (DMA) requirements for sites running Google AdSense.

The banner asks whether you consent to:

• Personalized advertising (using cookies and identifiers to tailor ads to you).
• Ad and content measurement, audience research, and product development by Google and its advertising partners.

You can choose Consent, Do not consent, or use Manage options to make granular choices per vendor and per purpose. Your choice is recorded by the CMP and applies on subsequent visits until you clear cookies or change your choice. To change your choice later, you can re-open the consent banner from the “Manage cookie preferences” control that the CMP exposes, or clear cookies for reefcalcs.com in your browser.

The CMP also controls Google Analytics 4. We use Google's Consent Mode v2 with all four required signals (ad_storage, ad_user_data, ad_personalization, analytics_storage) set to “denied” by default. If you consent, GA4 sets cookies and reports your session to us in aggregated form. If you do not consent, GA4 still reports a small set of cookieless pings (the “modeled” conversions feature) which contain no identifiers and cannot be used to track you across sites.

If you choose “Do not consent,” non-personalized ads may still be shown. Non-personalized ads use contextual signals (such as the topic of the current page) rather than your past activity, and they are permitted under GDPR without consent.

The legal basis we rely on for processing personal data via the ad network in these regions is your consent (GDPR Article 6(1)(a)). You can withdraw consent at any time, and doing so does not affect the lawfulness of processing carried out before withdrawal.

California residents (CCPA / CPRA)

reefcalcs does not sell personal information for money. Under the CCPA/CPRA, the term “sell” and “share” can include the disclosure of identifiers (including online identifiers and cookie IDs) to advertising partners for cross-context behavioral advertising. To the extent that the use of Google AdSense on this site constitutes “sharing” under the CPRA, California residents have the right to opt out. You can do so by enabling the Global Privacy Control (GPC) signal in your browser, which we honor, or by visiting Google Ads Settings to opt out of personalized advertising.

What we don't do

• No account is required to use the calculators.
• We never store your password in plaintext — only a bcrypt hash.
• We don't collect your calculator inputs; the math runs in your browser.
• No selling, sharing, or licensing of personal data we collect to third parties for their own marketing.

Email

If you email hello@reefcalcs.com, that message is delivered to the operator via Cloudflare Email Routing. The contents of the email are subject to whatever email provider you used to send it and whatever provider the operator uses to receive it. We will never sign you up for anything based on emailing in.

Third-party services we use

• Vercel — hosts the site and runs analytics. See their privacy policy.
• Neon — hosts the Postgres database that stores account data (email, password hash, saved tanks, parameter logs) when you create an account. See their privacy policy.
• Resend — sends transactional account email (verification, password reset, welcome, and the optional weekly digest). See their privacy policy.
• Cloudflare — manages DNS and forwards email to hello@reefcalcs.com. See their privacy policy.
• Amazon Associates — if you click an affiliate link to Amazon, Amazon may set cookies and collect data per their privacy policy.
• Google AdSense — serves the ads on this site and operates the consent banner shown to EEA / UK / Swiss visitors. See Google's privacy policy and advertising technologies overview.
• Google Analytics 4 — counts unique visitors and measures page usage so we know which pages need work. IPs are anonymised before storage, and the CMP controls whether analytics cookies are set. See Google Analytics's data practices.

Embedded calculators

The calculator pages at /embed/<name> are designed for third-party sites to iframe. Those embeds load the same calculator JavaScript directly from reefcalcs.com. The host site cannot read your inputs or results because of standard browser iframe isolation. We do not collect analytics on embedded calculator loads.

Changes to this policy

If we change how we collect or use data, the date at the top of this page will move. The substantive practices — calculations run in your browser, accounts are optional, and we set no first-party tracking cookies — are intentional and are not expected to change.

Contact

Questions about this policy: hello@reefcalcs.com.