Algae

Algae problems can be frustrating, especially when you're doing everything "right" and still end up with a green mess. The truth is, aquariums are complex ecosystems, and algae can be a symptom of subtle imbalances that aren't always obvious. This guide isn’t meant to be the last word on algae control, but it should help you begin identifying what might be causing your outbreak—and how to correct it thoughtfully.

Before jumping into fixes, it's important to understand that algae is a natural part of any healthy aquatic environment. The goal isn’t to eliminate algae entirely, but to keep its growth in check by addressing the underlying causes rather than just treating the symptoms.

Where to Start?

Avoid a "shotgun" approach. Making too many changes at once can actually destabilize your tank further, sometimes triggering different types of algae. In some cases, the best action is no action—algae can and often will burn itself out once the imbalance is corrected. But how do you know when to intervene?

Most algae issues stem from one or more of the following:

1. Excess light

2. The “ugly phase” of a new tank

3. Excess nutrients (especially nitrate and phosphate)

Let’s break each one down.

Excess Light

Algae are phototrophic—they use light to grow. If your lighting is too strong or runs for too long, you're essentially feeding algae. In a stable tank, 10–12 hours of light may be fine. In tanks with algae problems, aim for 6–8 hours per day.

If algae is really out of control, consider a blackout period. Turning the lights off for 4+ days can help suppress algae. Unlike plants, which have energy reserves and can tolerate short periods without light, algae are opportunistic and burn out quickly in low-light conditions.

Consider Ambient Light

Don't forget about sunlight or stray room light. If your tank lights are only on at night, but the tank gets sun or ambient light during the day, algae will still take advantage of that. Ideally, your lighting schedule should align with your home’s day/night cycle to help your fish maintain a healthy circadian rhythm.

New Tank Syndrome/Ugly Phase

If your tank is new, a bloom of diatoms or algae is almost inevitable. This is often the first visible sign that your tank is cycling and beginning to support life. In marine systems, this is known as the "ugly phase."

New substrates and equipment often leach silicates and nutrients that encourage algae growth. The good news? It usually resolves on its own within a few weeks to months. If the problem persists beyond that, it's time to evaluate lighting and nutrient levels more closely.

Excess Nutrients

Even if your water looks clear, high levels of nitrate (NO₃⁻) and phosphate (PO₄³⁻) can silently fuel algae. These compounds typically come from two sources:

• Decaying organic matter (uneaten food, dead plants or animals)

• Fish waste (a natural byproduct of feeding)

Overfeeding is a common culprit. Even food that gets eaten contributes to nutrient buildup—it just takes longer. Cutting back your feeding schedule is often one of the easiest and most effective ways to reduce nutrient levels. Most tropical fish can easily go a day or two without food and feeding once per day is more than enough in a healthy, mature tank.

Matching Import with Export

Feeding is nutrient import. Water changes and filtration are your export. To keep algae at bay, your export needs to keep up. If you're feeding daily but only changing water weekly—or inconsistently—you may be giving algae the upper hand.

Other Issues

If you're doing everything "right" and algae still keeps returning, there may be other variables at play:

Fertilizers and Additives

Plant fertilizers can sometimes cause imbalances if they supply too much of one nutrient and not enough of others. Algae tend to thrive in environments with excess macronutrients but lacking the trace elements that plants need. Be mindful of what you're dosing—and why.

pH Buffers

Some pH buffers, especially phosphate-based ones, directly add phosphate to your system. If you’re using a product to stabilize pH and still seeing algae, check the label. Remember: stability is more important than hitting a specific number. Many freshwater and marine species can adapt to a range of pH values, so long as that pH is consistent.

When There’s No Clear Cause

Sometimes algae appears despite your best efforts. Subtle, undetectable changes in water chemistry can trigger temporary blooms. In those cases, patience is key. If you've addressed the big three—light, nutrients, and new tank instability—algae will usually taper off as your system rebalances.

The most effective long-term strategy for algae control is to identify and resolve the root cause. Once that’s handled, let nature take its course. Algae will decline as conditions become less favorable.

When There’s No Clear Cause

Sometimes algae appears despite your best efforts. Subtle, undetectable changes in water chemistry can trigger temporary blooms. In those cases, patience is key. If you've addressed the big three—light, nutrients, and new tank instability—algae will usually taper off as your system rebalances.

The most effective long-term strategy for algae control is to identify and resolve the root cause. Once that’s handled, let nature take its course. Algae will decline as conditions become less favorable.