What setup mistakes should I avoid before cycling?
When: Right before you start cycling
Short answer: The setup stage isn't done until salinity holds ~1.025 sg and temperature holds 76-78°F for a few days with everything running — heater, flow, light, all of it. The single biggest mistake is treating "the tank is full and looks fine" as that signal; run a full leak test first, verify with a refractometer and thermometer (not a swing-arm hydrometer or the heater's own dial), and don't start dosing ammonia until both numbers are actually stable.
The details
Pulling together the mistakes named across this stage's cards, in the order they tend to bite:
- Skipping the leak test. Run the tank full for at least 24-48 hours, on its final level stand, before trusting it — a slow leak found empty is an inconvenience; found full of saltwater and rock is a flood.
- Using tap water anywhere in the process. Named repeatedly as a top mistake across both standard and nano tank content — it undermines the RO/DI work you just did.
- Trusting a swing-arm hydrometer or the heater's built-in dial instead of a refractometer and a separate thermometer.
- Running with a single heater and no backup. The most repeated single cause of beginner tank crashes in this corpus.
- Declaring the tank "stable" off one good reading. The gate is salinity and temperature holding for a few days with everything running — powerheads, heater, light — not a one-time snapshot.
- Starting the ammonia dose for cycling before the box itself is stable. Cycling bacteria need a stable environment to establish; a still-swinging tank never cycles cleanly.
The numbers
| Gate condition | Target |
|---|---|
| Salinity | ~1.025 sg, holding for a few days |
| Temperature | 76-78°F, holding for a few days |
| Leak test | Full, on final stand, 24-48+ hours |
| Everything running | Heater, flow, light — not a partial setup |
Common mistakes
- Moving straight from "filled" to "dosing ammonia" without a stability check first.
- No backup heater, no separate thermometer, no refractometer — see temperature-and-heater-basics and how-to-mix-saltwater.
- Using tap water at any point — see ro-di-water-why-not-tap.
When to worry
- Normal: Salinity or temperature needing a day or two of small adjustments right after filling — that's expected while everything settles in.
- Worry: Either number still drifting after several days with the full system running, or any leak found during the fill test — fix both before moving on.
What's next
Once salinity and temperature both hold steady for a few days, the setup stage's gate is met — move on to growing your biological filter in nitrogen-cycle-explained.
- Salinity or temperature still drifting after a few days with everything running
- Any leak found during the initial fill test
- Reef Knowledge Base — Common Mistakes (using tap water instead of RO/DI)
- Reef Knowledge Base — Nano Tank Mistakes
- Reef Knowledge Base — Leak Testing a New Saltwater Aquarium (BRStv Beginner EP10)
- Reef Tank Cycling Research — heater/salinity setup before cycling begins