Diatoms are a type of algae that can quickly take over a saltwater aquarium, covering surfaces with a dusty brown film. While not necessarily harmful, diatom blooms can be unsightly and difficult to get rid of.
However, with some effort, you can eliminate existing diatoms and prevent future outbreaks in your tank.
What are diatoms?
Diatoms are single-celled, photosynthetic algae encased in glass-like cell walls made of silica. There are over 100,000 species found throughout aquatic and damp environments.
It requires silicon to construct its cell walls. They also need other nutrients, like nitrogen and phosphorus, for growth.
In aquarium systems, diatoms efficiently absorb dissolved silicates from tap water and waste to propagate.
Their rapid reproductive cycle allows them to multiply faster than competing algae. Diatom blooms usually happen in new tanks going through the initial break-in cycle or if water parameters fluctuate.
While diatoms themselves aren’t harmful, allowing them to thrive can have detrimental effects. As vast colonies die off, bacteria decompose the cells and consume more oxygen.
This can suffocate animals or feed cyanobacterial growth. Getting diatoms under control early is key.
How do I eliminate and prevent diatoms?
If your saltwater tank suffers from visible diatom buildup, take action immediately. Several methods exist to kill and manually remove established growths.
Consistently eliminating diatoms and their ability to reproduce is important for resolving the underlying cause.
Use a New Toothbrush
A brand new, unused toothbrush with firm bristles easily scrubs off diatom films from decorations and tank walls. Simply scrub away any visible brown material. Repeat daily until algae no longer return as quickly.
Do a Deep Sand Bed Vacuum
Use a gravel vacuum to deeply clean the entire sand bed surface. Stir up all the debris until the water runs almost clear. This removes nutrients trapped in the substrate, so diatoms have less to feed on.
Clean or Replace Filter Media
Dirty filter pads, floss, and other media can export excess silicates, phosphates, and nitrates, fueling diatom blooms. Thoroughly rinse reusable media in old tank water every few weeks. Replace disposable media regularly.
Use a Powerhead on Output Mode
Aim a powerhead in pulse or output mode at affected areas to create targeted currents that will lift diatoms off surfaces. Combine it with manual scrubbing for efficiency. Monitor corals or other animals sensitive to higher flows.
Do a 3-4 Day Blackout
For severe cases unresolved by scrubbing, try covering the tank to block all light. Shut off lights, wrap the background and sides with dark towels or cardboard, and turn off active lighting periods too.
Healthy tanks can handle 3–4 days without adverse effects. Light starvation inhibits algae growth, so diatoms decline.
Use Phosphate Removal Media
High phosphate encourages diatom propagation. Chemical filter media like PhosGuard or activated alumina granules help remove phosphates from system water, limiting the nutrients available. Replace every few weeks when saturated.
Introduce clean-up crews.
Certain saltwater aquarium fish or live rock hitchhikers will munch away at diatom films. Snails like nerites, ceriths, or trochus, along with herbivores like tangs or rabbitfish, can be effective grazers over time
Spot Treat with Peroxide or Algaecide
In small tanks, using a syringe or pipette to spot treat stubborn diatom patches with low percentages of hydrogen peroxide (1–5%) or red slime remover can kill growth. Do not overapply it near sensitive fish.
Maintain Stable Water Parameters
Fluctuating ammonia, nitrites, phosphates, nitrates, and pH commonly encourage algae growth. Keep all levels within acceptable ranges through routine testing and water changes. Diatoms particularly feed on high silicates and phosphates.
Upgrade Filtration System
Robust biological, chemical, and mechanical aquarium filtration handles nutrient export and water polishing necessary to starve opportunistic algae-like diatoms.
Consider adding a protein skimmer, plenum, better pumps, extra filter media capacity, etc. if issues continue.
Feed Sparingly
Overfeeding provides excess fish waste nutrients utilized by diatom algae. Offer slow-sink pellets just once or twice daily in amounts completely eaten within a few minutes. Target-feed herbivores for increased husbandry control.
Maintain high-flow Areas
Improve aquarium circulation with multiple turnover points to prevent dead spots where detritus collects, fueling algae growth. Strategically arranged powerheads prevent sediment accumulation, promoting diatom recurrence after manual removal.
Stay on Top of Routine Maintenance
Don’t skip water changes, filter media cleaning, protein skimming, glass algae scrubbing, and other tasks that allow organics and nutrients to accumulate.
Consistency helps stabilize conditions unfavorable to diatom blooms. Limit lighting periods to 8 hours daily without promoting other nuisance algae instead.
Quarantine All New Livestock
Invertebrates or fish introduced by wholesalers often harbor illnesses from transport stress and contaminated holding systems. Isolate new arrivals for 60–90 days, eliminating pathogens or parasites brought in before adding them to displays.
Avoid Overstocking
Excess fish, coral, and critters pollute water through metabolic waste above biofilter capacity. Overcrowding intensifies maintenance needs, water quality instability, and algae growth, including diatoms. Allow 1-2 small fish or 1” total-length livestock per 5 gallons.
Final Words
The key to preventing future diatom outbreaks lies in maintaining pristine and stable water quality through filtration media upgrades and export methods such as refugium and protein skimming, in conjunction with limiting nutrient availability.
Manual removal, combined with allowing herbivores and clean-up crews to continually graze, keeps problematic growth in check once underlying sources are addressed.
Stay vigilant with tank maintenance, and diatoms shouldn’t return!
FAQ
Are diatoms harmful to my fish or corals?
Not necessarily, but allowing them to spread uncontrolled can lower oxygen levels as they die off and decay. They also indicate an underlying water quality issue.
What is the fastest way to kill diatoms in my aquarium?
A 3- to 4-day complete blackout by wrapping the tank with dark bags or cardboard to light starve the algae is very effective. Combine with activated carbon dosing.
What fish or inverts will eat diatom algae?
Many snails, like nerites, trochus, and ceriths, enjoy grazing on diatom films. Tang and rabbitfish algae grazers are also good choices. Avoid overstocking, though.
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