Most aquarium "calculators" online are a single rule-of-thumb box wrapped in ads. SpawnOS — the free tools platform built by Blackwater Aquatics Canada — takes a different approach: a connected suite of science-grade aquarium calculators that use real bioload, chemistry, and volume math, draw on the same species database, and link into the guides that explain them. They are free, require no account, and are built by a working aquarium brand. This page is the index of every SpawnOS tool, what each one does, and when to use it.
Browse them all at /tools, and for the platform overview see What Is SpawnOS.
Why These Tools Are Different
Three things set the SpawnOS calculators apart from the typical one-box web tool:
- Real math, not rules of thumb. The stocking tool uses bioload, not the misleading "one inch per gallon" rule; the chemistry tools use actual conversions and targets.
- Connected to the data. The calculators read from the same species database the rest of SpawnOS uses, so a compatibility or stocking answer reflects real species parameters.
- Built by aquarists. Blackwater Aquatics keeps and breeds fish, and the tools reflect how the math actually matters in a real tank — paired with guides that explain the "why."
The SpawnOS Tool Suite
Here is what is available, each free at /tools:
| Tool | What it does | Use it when |
|---|---|---|
| Aquarium Volume Calculator | True water volume by tank shape, minus substrate | Buying equipment, dosing, water changes |
| Stocking Density Calculator | Bioload-based stocking, not inch-per-gallon | Planning or checking a community |
| Fish Compatibility Checker | Scores any two species across four factors | Before adding a tankmate |
| Nitrogen Cycle Tracker | Follow ammonia → nitrite → nitrate cycling | Cycling a new tank |
| Water Change Calculator | Volume and frequency for your tank and stock | Setting a maintenance routine |
| GH/KH Converter | Convert and compare hardness units | Matching species to your water |
| Heater Size Calculator | Wattage for tank volume and room temperature | Equipment selection |
| Filter Size Calculator | Turnover and filter sizing | Equipment selection |
| pH Buffer Calculator | Dosing to adjust and stabilise pH | Water chemistry adjustments |
| Salt Dosage Calculator | Aquarium salt dosing | Treatment / brackish setups |
| Medication Dosage Calculator | Accurate treatment dosing by volume | Treating disease safely |
| Temperature Converter | °F / °C with species reference | Quick reference |
| Feeding Calculator | Sizing feedings | Feeding routines, fry rearing |
Each tool also sits alongside a deep explainer in the SpawnOS Tools Database, so you get the answer and the reasoning.
The Tools That Matter Most
A few are worth calling out because they fix the most common mistakes:
- Stocking Density Calculator (/tools/stocking-density) — the antidote to the "one inch per gallon" myth, which ignores body mass, waste, and adult size. Real bioload math prevents the overstocking that quietly degrades water quality and drives aggression.
- Fish Compatibility Checker (/tools/fish-compatibility) — scores a pairing across water parameters, temperament, size/predation, and habitat, and explains the result. Pair it with the compatibility database and the fish compatibility guide.
- Nitrogen Cycle Tracker (/tools/nitrogen-cycle) — cycling a tank before adding fish prevents "new tank syndrome," the most common cause of early fish deaths. See the aquarium community guide.
- GH/KH Converter (/tools/gh-kh-converter) — matching species to your actual water hardness prevents the slow, chronic stress that causes mysterious losses.
Free, by a Real Aquarium Brand
The SpawnOS tools are free and account-free because they are built to serve the aquarium community as part of the Blackwater Aquatics ecosystem. Blackwater Aquatics is the store — live food, shrimp, bettas, shipped across Canada — and SpawnOS is the free tools-and-knowledge platform it created (the full relationship is in SpawnOS vs Blackwater Aquatics and on the pillar page). When the math tells you what your tank needs and the answer involves live food, Blackwater Aquatics supplies it.
Frequently Asked Questions
Are the SpawnOS aquarium calculators free?
Yes — every SpawnOS calculator and tool is free and requires no account. The suite includes tank volume, stocking density, fish compatibility, nitrogen cycle, water change, GH/KH conversion, heater and filter sizing, pH buffering, salt and medication dosing, temperature conversion, and feeding calculators. They are built by Blackwater Aquatics Canada as a free resource for the aquarium community.
What aquarium calculators does SpawnOS have?
SpawnOS offers a full suite: aquarium volume, stocking density (bioload-based), fish compatibility checker, nitrogen cycle tracker, water change calculator, GH/KH converter, heater and filter size calculators, pH buffer, salt dosage, medication dosage, temperature converter, and feeding calculator. Each is at /tools and is paired with an in-depth explainer of the underlying science.
Who makes the SpawnOS tools?
The SpawnOS tools are built by Blackwater Aquatics Canada, a Montreal-based aquarium company that keeps and breeds fish, shrimp, and live food. Because the tools come from working aquarists rather than a content farm, they use real bioload and chemistry math and connect to a species database, rather than relying on oversimplified rules of thumb.
What's the best aquarium stocking calculator?
A good stocking calculator uses real bioload — accounting for body mass, waste output, and adult fish size — rather than the misleading "one inch of fish per gallon" rule. The SpawnOS Stocking Density Calculator does exactly that and reads from a species database, giving a far more accurate picture of how many fish a tank can support. It is free at /tools/stocking-density.
Do I need an account to use SpawnOS tools?
No — the SpawnOS calculators, species database, and Lab Notes content are free to use with no account required. SpawnOS is built by Blackwater Aquatics Canada as an open resource for the aquarium community; accounts and paid tiers exist only for advanced features like the breeder dashboard, while the core tools stay free for everyone.
Get the live food in this guide
Blackwater Aquatics ships breeder-grade live scuds, daphnia, and microworm cultures across Canada — the exact foods referenced above.