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How it works · 23 live rules
Reef tank compatibility checks, shown in public.
ReefCrafter runs deterministic rules for skimmer headroom, heater safety, return flow, display flow, light coverage, and missing support gear. This page shows what the checker evaluates before you open the planner or buy a part.
Methodology
How the engine actually decides.
ReefCrafter is a deterministic checker, not a recommender. It reads the build you assembled, runs each rule against published specs and well-known reef-keeping benchmarks, and shows you what fired and why. Same input, same output — every time.
Step 01
Read the build
The engine pulls real values from the gear you added: skimmer rated_max_gallons, total heater wattage, return-pump GPH, light count and footprint, plus tank gallons, reef goal, and bioload tier. No hidden inputs.
Step 02
Run every applicable rule
Each rule has an applies_when filter and a condition (LHS op RHS). Heater rules don't fire unless tank gallons are set. Skimmer rules scale by bioload tier. Rules that don't apply are skipped, not silently downgraded.
Step 03
Show what fired and why
Every finding links back to its rule key and the values it pulled from your build. Warnings can be overridden with a written reason that stays attached to the saved build. Hard-physics safety rules can't be silenced.
Where the rules come from. Manufacturer-published spec sheets (skimmer rated capacity, heater wattage, fixture coverage), accepted reef-keeping benchmarks (turnover multipliers by reef goal, the 2.5–5 W/gal heater band, the +1 skimmer rule), and physics that doesn't care about opinions (head loss, footprint coverage). No machine learning. No scraped reviews. No ratings averaged from anonymous strangers.
Severity
Three classes of finding.
Every rule fires at one of three severities. Errors block the build until you address them; warnings and advisories don't.
Errors · 2 live
Real risks — cooked livestock, flooded floors, broken gear. The build shouldn't ship until these are addressed.
Warnings · 13 live
The build will work but you're at the edge of recommended specs. Step up the gear if you can.
Advisories · 8 live
Community wisdom. AIO + SPS is harder. Single-light SPS is suboptimal. Worth knowing, not blocking.
The rules
What the engine actually checks.
Every rule is documented here. Click into a build and the planner fires these against your spec live; the warning shows the exact rule key and the values it pulled from your build.
Declarative, not magical.
Each rule is a JSON object with a key, a severity, and a condition. No ML, no "trust us." If a rule fires on your build you can read the condition and verify it matched.
Re-runs on every change.
Swap the tank, all downstream rules re-evaluate. Skimmer rating rechecked, flow turnover recomputed, heater band reassessed. No stale numbers.
Documented, not magical.
The full ruleset is summarized below by category, with the rule key, severity, and what each check actually does. Spot a rule that's wrong, or one we're missing? Email rules@reefcrafter.com. Suggestions are reviewed against published specs and accepted practice before they ship — input shapes the backlog, it doesn't auto-publish.
Tank + Stand · 3 rules
Display volume, sump volume, stand load, and footprint. The tank is the constraint everything else has to live inside.
AIO + SPS-dominant warning
aio_sps_advisory
Nano + SPS-dominant warning
nano_sps_advisory
Tanks 75g+ concentrate floor load above residential rating
tank_floor_load_residential_advisory
Lighting · 6 rules
PAR coverage matched to your tank footprint. Corner shadowing flagged. Light count vs SPS-tier coverage required.
Total light coverage area meets tank footprint
light_coverage_meets_footprint
PAR at 18in meets soft-coral target
light_par_softie_target
PAR at 18in meets mixed-reef target
light_par_mixed_target
PAR at 18in meets SPS-dominant target
light_par_sps_target
SPS-dominant builds usually want multiple light fixtures
sps_single_light_advisory
Light coverage at least 50% of tank footprint (geometric floor)
light_coverage_geometric_minimum
Return Pump · 2 rules
Real GPH after head-loss, not box rating. Quiet-mode throughput counted separately.
Return pump GPH provides minimum 5x turnover
return_pump_min_turnover
Return pump may be overpowered for system
return_pump_overpowered_advisory
Protein Skimmer · 4 rules
Rated capacity scaled by your bioload tier. A skimmer that "fits the gallons" isn't enough if the bioload is heavy.
Skimmer rating sufficient for light bioload
skimmer_rating_light_bioload
Skimmer rating sufficient for medium bioload
skimmer_rating_medium_bioload
Skimmer rating sufficient for heavy bioload
skimmer_rating_heavy_bioload
AIO skimmer fitment warning
aio_skimmer_fitment_warning
Flow / Powerheads · 4 rules
Total turnover by reef type — 10× softie, 30× mixed, 40×+ SPS. Glass-mount vs gyre placement noted.
Total flow meets softie/LPS turnover target (10-20x)
total_flow_softie_target
Total flow meets mixed-reef target (20-30x)
total_flow_mixed_target
Total flow meets SPS-dominant target (40-50x)
total_flow_sps_target
AIO + extra powerhead usually unnecessary
aio_powerhead_advisory
Heating / Temperature · 3 rules
Watts per gallon held inside the safe band, with redundancy required on tanks 50g and up.
Total heater wattage meets minimum (2.5 W/gal)
heater_wattage_floor
Total heater wattage not dangerously high
heater_wattage_ceiling
Tanks 50g+ should have at least 2 heaters
heater_redundancy_50g_plus
ATO + Dosing · 1 rule
Reservoir capacity vs evap rate. Dosing-pump throughput vs daily demand for two-part / kalk regimes.
ATO recommended for tanks 30g+
ato_recommended_30g_plus
What the engine can’t do
The honest limits of a pre-buy check.
ReefCrafter is a sanity check on the gear and goals you wired into the planner. It is not omniscient and it is not a replacement for the slow parts of reef-keeping.
It only sees what you entered.
The engine reads your tank gallons, gear, reef goal, and bioload tier. It can't see your room temperature, your water source, your maintenance habits, your acclimation routine, or your real-world flow patterns once rockwork is in.
The ruleset is hardware-first.
Most live rules cover gear sizing. Livestock-specific compatibility checks are in the planner and still expanding. A clean compatibility report is not a green light to add aggressive fish or sensitive corals on day one.
Manufacturer ratings are optimistic.
Skimmer 'rated for' values, light coverage claims, and pump GPH numbers are best-case figures. The engine deliberately scales them by bioload, head loss, and reef goal — but no rule replaces watching your actual tank.
It can’t cycle your tank for you.
Compatibility passing means the build is internally consistent. It does not mean the tank is ready for livestock. Cycling, parameter stability, and slow stocking still matter — and always will.
The ruleset is evolving.
ReefCrafter is in open beta. New rules ship as we hit edge cases the engine missed; existing rules get tightened when they fire too aggressively. Saved builds re-evaluate against the current ruleset, so today's pass can become tomorrow's warning.
It doesn’t pick a winner for you.
The engine flags risk; it doesn't rank brands or tell you the 'best' skimmer. Vendor links exist when ready, but the recommendation is whatever fits the build — not whatever pays the highest commission.
How to read findings responsibly. Treat errors as a hard stop until addressed or explicitly overridden with a written reason. Treat warnings as a step-up-if-you-can nudge, not a guarantee the build will fail. Treat advisories as worth reading but not blocking. And treat a clean report as a useful checkpoint — not a substitute for the patience reef tanks demand.
Help us tighten the rules
Push back on a rule. We’d rather hear it now.
Reef-keeping accumulates know-how that no spec sheet captures. If a rule fires on a build you know works, or stays quiet on a build you know doesn’t, tell us. Suggestions, edge cases, and long-tank experience all feed the backlog.
Important: ReefCrafter is not a crowdsourced engine. Every suggestion is reviewed against published specs, manufacturer data, and accepted reef-keeping practice before anything ships. Community input shapes the backlog — it does not auto-publish rules.
What good rule feedback looks like
- The build: tank gallons, reef goal, the specific gear, and bioload tier.
- The finding: which rule fired (or didn’t) and what you expected instead.
- The math: the ratio, threshold, or spec reference behind your suggestion.
- The receipts: manufacturer link, long-running tank context, or a published reef-keeping source where possible.
Diagnostic guides
Turn the rules into pre-buy checks.
If you are not ready to open the full planner yet, start with the expensive weak spots: skimmer capacity, flow, lighting, heaters, and the final cart review.
Try it
Check a reef build. Then buy with fewer surprises.
Use the build checker for a quick diagnostic, or open the full planner when tank size, livestock, gear, and budget all need to agree.