Aquarium Cycling Guide (Freshwater & Saltwater)

Recommended Bottled Bacteria

• Dr. Tim's One & Only (fresh & marine)
• FritzZyme 7 (freshwater)
• FritzZyme 9 (saltwater)
• Seachem Stability (fresh & salt)
• Brightwell MicroBacter7 (fresh & salt)

RO/DI vs Municipal Tap Water

RO/DI water:

• Strongly recommended for saltwater.
• Optional for freshwater; may require re-mineralization.
• Saltwater must be mixed using RO/DI and verified with a hydrometer or refractometer.

Municipal tap water

• Always treat for chlorine and chloramine.
• Common conditioners: Seachem Prime, Fritz Complete, API Tap Water Conditioner.
• Dose for full tank volume.
• Never cycle with untreated tap water.

Skimmer & Light Settings During Cycling

Saltwater skimmer:

• Fishless: skimmer on.
• Fish-in: skimmer on.
• Follow bacteria instructions if they say skimmer off for 24 hours.

Light settings

• General rule: low light only.
• Freshwater planted: low intensity, 6–8 hours.
• Freshwater non-planted: very dim or off.
• Saltwater rock-only: low or off.
• Saltwater with corals: reduced intensity and shorter photoperiod.

Freshwater Fish-In Cycle

Recommended hardy fish (including nano):

• Zebra danios
• White cloud mountain minnows
• Platies
• Guppies
• Cherry barbs
• Corydoras (added later)

1. Set up tank, filter, heater, decor.
2. Fill with treated tap water or RO/DI.
3. Add a small number of hardy fish.
4. Add bottled bacteria.
5. Test daily.
6. Keep ammonia and nitrite under 0.25–0.5 ppm.
7. Do 25–50 percent water changes if levels rise.
8. Cycle time: 2–6 weeks.
9. Cycle complete when ammonia and nitrite stay at zero for a full week.

Freshwater Fishless Cycle

1. Set up tank and dechlorinate.
2. Add bottled bacteria.
3. Dose ammonia to ~2 ppm.
4. Test every 1–2 days.
5. Re-dose ammonia when below ~1 ppm.
6. Keep ammonia and nitrite under 5 ppm.
7. Cycle time: 3–6 weeks (1–3 weeks with strong bacteria).
8. Completion test: dose to 2 ppm and confirm ammonia and nitrite hit zero in 24 hours.
9. Do a 50–80 percent water change before adding fish.

Saltwater Fish-In Cycle

Recommended hardy fish (including nano):

• Captive-bred ocellaris or percula clownfish
• Firefish
• Banggai or pajama cardinalfish
• Chromis (with caution)

1. Mix saltwater with RO/DI to 1.024–1.026.
2. Add rock, sand, heater, circulation.
3. Confirm salinity with a hydrometer or refractometer.
4. Add a small number of hardy fish.
5. Add bottled bacteria.
6. Run skimmer.
7. Keep lights low or off.
8. Test daily.
9. Keep ammonia and nitrite under 0.25–0.5 ppm.
10. Cycle time: 3–6 weeks.
11. Cycle complete when ammonia and nitrite stay at zero for a full week.

Saltwater Fishless Cycle

1. Mix saltwater with RO/DI.
2. Add rock, sand, heater, circulation.
3. Confirm salinity with a hydrometer or refractometer.
4. Add bottled bacteria.
5. Dose ammonia to ~2 ppm.
6. Run skimmer.
7. Keep lights low or off.
8. Test every 1–2 days.
9. Re-dose ammonia when below ~1 ppm.
10. Cycle time: 3–6 weeks (1–3 weeks with strong bacteria).
11. Completion test: dose to 2 ppm and confirm ammonia and nitrite hit zero in 24 hours.
12. Do a 50–80 percent water change before adding fish or corals.

What to Expect & Simple Troubleshooting

Normal signs during cycling:

• Cloudy water
• Brown biofilm or diatoms
• Rising nitrate levels

If ammonia or nitrite stall

• Check pH
• Ensure filter is running properly
• Keep ammonia and nitrite under 5 ppm
• Add bottled bacteria
• Do a partial water change and re-dose ammonia to 2 ppm (fishless only)

If fish show stress in fish-in cycles

• Test immediately
• If ammonia or nitrite exceed 0.5 ppm, do a 50 percent water change
• Reduce feeding
• Add bottled bacteria

If more help is needed

Email or text us for guidance or interpretation of test results. Visit /contact for our email and phone number — we're happy to walk you through it step by step.