If you're wiping your aquarium glass clean only to watch it film over again days later, the glass isn't the problem; it's a symptom. Persistently dirty glass almost always points to an imbalance in light, nutrients, or maintenance. Here's how to diagnose and fix it for good.
First, Identify What's on the Glass
Green film or spots
This is algae, driven by light and nutrients. Green dust algae forms a fine film; green spot algae forms hard, raised dots.
Brown, dusty coating
This is diatoms, brown algae, extremely common in new tanks as they balance out. It usually fades on its own within the first few weeks.
A clear, slippery film
This can be a bacterial or biofilm layer, often linked to surface scum and low water movement.
The Three Root Causes
- Too much light: long lighting periods or direct sunlight are the number one cause of algae on glass
- Excess nutrients: overfeeding, overstocking, or infrequent water changes leave nitrate and phosphate that algae feed on
- Insufficient maintenance: stretched-out water changes let nutrients accumulate
💡 Pro tip: If your tank gets any direct sunlight during the day, move it. Sunlight is almost impossible to out-compete and is the most common hidden cause of relentless algae.
How to Fix It
- Put your lights on a timer and limit them to 6–8 hours per day
- Move the tank out of any direct sunlight
- Cut feeding back and remove uneaten food after two minutes
- Increase the frequency of partial water changes to lower nitrate
- Add fast-growing live plants to out-compete algae for nutrients
- Consider algae-eating livestock such as nerite snails or otocinclus
Cleaning the Glass Properly
- Use a magnetic scraper or algae pad, never a household sponge (soap residue is toxic)
- For hard green spot algae, use a blade scraper (plastic blade on acrylic tanks to avoid scratches)
- Clean the glass just before a water change so loosened algae gets siphoned out
The Takeaway
Don't fight the glass; fix the balance. Reduce light, reduce nutrients, and stay consistent with maintenance, and you'll spend far less time scraping and far more time enjoying a crystal-clear tank.
Find algae scrapers, timers, and water care products in our Aquatics range.
