Equipment guide
Circulation & Flow
Why moving water to every corner matters, and how to kill dead spots.
TL;DR, Circulation & Flow
Flow does more than the filter alone. It carries CO2, nutrients and heat to every plant and stops waste settling into dead spots where black beard algae and anaerobic pockets form. You want gentle, even movement that reaches all corners, not a wind tunnel that pins the fish and flattens the plants. A little surface agitation or a skimmer keeps the film off the top and gas exchange up, and a small powerhead fixes dead corners in a bigger tank. In a CO2 tank especially, good flow is what actually delivers the gas to the leaves.
Reading your flow
- The goal
- Gentle, even movement to every corner
- Detritus or BBA in one spot
- A dead spot, aim flow there
- Fish struggling, plants flattened
- Too much flow, ease it off
- Oily film on the surface
- Add agitation or a skimmer
- CO2 tanks
- More surface agitation off-gasses CO2, balance it
Why flow matters
The filter's job is not just to clean, it is to move water. Even circulation spreads CO2, nutrients and warmth to every plant and keeps detritus suspended long enough to reach the filter instead of rotting in a corner. Where flow is weak, waste settles, oxygen drops, and black beard algae and cyanobacteria move in. The goal is gentle, even movement everywhere, not brute force. Too much flow is its own problem: fish fight the current, carpets lift, and delicate plants get battered.
Surface agitation and skimmers
A little movement at the surface breaks up the oily film that can form there and drives gas exchange, pulling oxygen in, which matters most at night when plants stop producing it. A surface skimmer, or simply angling the outflow up toward the surface, handles this. The trade-off in a CO2 tank is that surface agitation also off-gasses CO2, so you balance the two: enough movement for oxygen and a clean surface, not so much that you can't hold a stable CO2 level.
Finding and fixing dead spots
Watch where detritus settles and where algae favours one corner, those are your dead spots. Aim the filter outflow to push water along the back glass so it sweeps around the tank in a gentle loop, rather than firing straight across. A spray bar spreads flow more evenly than a single nozzle. In a larger or awkwardly shaped tank, a small powerhead or wavemaker aimed at the stagnant area clears it without cranking up the whole tank.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Why is algae only in one corner of my tank?
That corner almost certainly has weak flow. Detritus settles and black beard algae or cyanobacteria take hold where water is stagnant. Aim your outflow to sweep that area, or add a small powerhead, and it usually clears.
Do I need a surface skimmer?
It is not essential, but it keeps the surface film off and improves gas exchange, which helps oxygen levels. Angling the filter outflow up at the surface does much the same job for free.
Can I have too much flow?
Yes. If fish are pinned against the glass or struggle to swim, carpets lift, or delicate plants get battered, the flow is too strong. Aim for gentle movement everywhere rather than raw power.