Diatoms are single-celled microalgae with silica-based shells. Often seen as pests in newly cycled tanks, they actually play an essential role in marine ecosystems. Cultured intentionally, they're a valuable live feed for grazers like snails, chitons, certain copepods, and filter feeders.
What you'll need
- Diatom starter culture (e.g. Navicula, Thalassiosira, or Skeletonema)
- F/2 fertiliser or equivalent
- Silica source (sodium metasilicate or soluble sand)
- Saltwater at 1.018 to 1.022 SG
- Strong, full-spectrum light (6,500 to 10,000K, 12 to 16 hours per day)
- Air pump and rigid airline
Setup steps
Prepare your medium. Mix RO/DI water with reef salt to 1.020 SG. Add F/2 nutrients and a silica source (10 to 30 mg/L sodium metasilicate works well).
Inoculate. Add the diatom starter once temperature and salinity are stable.
Aerate. Use gentle aeration with a rigid airline to keep cells suspended and prevent settling on the bottom.
Lighting. Place the culture under a bright, full-spectrum source. Diatoms need solid light, though slightly less than what most green phyto strains demand.
Harvest. Within 5 to 10 days, the water should turn golden-brown. Diatoms tend to stick to surfaces, so swirl or scrape the sides gently to dislodge them. Harvest by decanting or running through a fine sieve.
Tips
- Use glass or plastic with smooth walls. Diatoms love to settle, and rougher surfaces give them more to grip.
- Avoid excess nutrients. Nitrate-heavy environments can crash a culture quickly.
- Refrigerate unused portions and use them up quickly to avoid die-off.
Why bother culturing diatoms?
They're not as commonly cultured as the standard phyto strains, but diatoms provide excellent nutrition, especially for early-stage filter feeders and certain snails. They're also a natural part of many marine food webs and can help condition grazers before sale or introduction to new tanks.
