Why does algae keep returning in my aquarium?
Written by
Wang Jiahao
Reviewed by
Prof. Henry Webster, Ph.D.Recurring algae troubles many aquarists, since temporary solutions overlook basic imbalances in an aquarium. The algae returns when the underlying issues, such as lighting/nutrient mismatch or filtration problems, are still present. I've kept multiple aquariums where green phases come and go until the systemic issues are tended to. Real solutions take full control of the ecosystem, not just scrubbing.
Persistent Imbalances
- Light excess: Photoperiods exceeding tank needs fuel regrowth
- Nutrient accumulation: Phosphate-rich tap water constantly replenishes algae food
- CO₂ fluctuations: Unstable levels stress plants allowing algae advantage
- Filter limitations: Undersized filters can't process waste efficiently
Corrective Actions
- Test tap water: Treat phosphate-heavy sources before changes
- Light audits: Measure PAR and reduce duration by 2 hours
- Filter upgrades: Increase media capacity by 30%
- Stable CO₂: Maintain 20-30 ppm with regulators
Check your tap water for hidden sources of phosphate. Municipal supplies should not contain more than 1-3 ppm of phosphates. Use a phosphate remover in your filters or switch to R.O. water. I check mine monthly and use a PhosGuard type of media, which stops a renewable source of nutrients for algae.
Audit biofilter capacity. Insufficient bacterial colonies = ammonia spikes shortly after fish have been fed. Add another 30% volume of filter media using porous ceramic rings, and cycle this media for at least 4 weeks before removing any old material. This will ensure that filtration remains intact during the upgrade.
Establish non-negotiable maintenance routines. For me, it involves vacuuming the substrate weekly as I perform my 30% water changes, cleaning the filter media monthly, and scraping the glass every three days. I have my phone set to remind me when it's time to do each. Without these little reminders, it's easy for small things to become chronic problems.
Tracking algae development using an algae log helps to record growth sites and rates on a weekly schedule. Water parameters should be tested before maintenance. While documenting the date, also track the lighting and feeding schedules. After 60 days, patterns will emerge that can help decipher which imbalances have continued, and address them with appropriate solutions.
Read the full article: Comprehensive Fish Tank Algae Control Guide
