Pumps
Flow is the most under-rated variable in a planted tank. Filtration gets the attention, but plenty of algae problems, poor CO2 response and stunted growth trace back to water simply not moving through parts of the tank. Powerheads, wavemakers, return pumps and air pumps all exist to fix that, and picking one is mostly about matching flow to the tank rather than buying the biggest number.
How much flow you need
For a planted tank running pressurized CO2, aim for roughly ten times the tank volume per hour in total turnover — a 40-gallon tank wants something in the region of 400 GPH between filter and powerheads combined. That figure is not about cleaning the water. It is about getting CO2-enriched, fertilizer-carrying water to every leaf in the tank before it degasses. A high-tech tank with weak circulation will show you exactly which corners are missing out, because that is where the black beard algae appears.
Low-tech and no-CO2 tanks need much less — four to six times turnover is plenty, and pushing more just stirs up substrate.
Distribution beats raw GPH
A dead spot is a dead spot regardless of how strong the pump is. Before adding another pump, watch where the plants move and where they do not; a single small powerhead aimed across the back wall often fixes more than doubling filter output. Cyanobacteria and detritus accumulation are both flow-distribution symptoms, not filtration symptoms.
Powerheads and wavemakers
These add circulation without adding filtration, which is usually what you actually want. Controllable DC models run quieter, draw less power and let you dial flow down — worth it in a display tank or a bedroom. AC models are cheaper and close to indestructible. Wi-Fi controllable units let you schedule pulse patterns and night-time reductions, which matters more for reef tanks but is pleasant in a big planted display too.
Return pumps and head height
If you are running a sump, remember that a pump's rated GPH is measured at zero vertical lift. Push the same pump four feet up to the display and you may lose a third or more of that. Check the pump's head-height curve against the actual distance from sump to tank rim before you buy, and size up rather than down — you can always throttle a pump back with a valve, but you cannot make it push harder.
When less flow is right
Bettas, fancy guppies, and anything with long finnage will fight strong current all day and lose condition doing it. Shrimp tanks with shrimplets want gentle flow and, ideally, sponge intakes. Blackwater and slow-water biotopes are meant to be still. In these tanks the answer is a sponge filter on an air pump, not a powerhead.
Air pumps, tubing and the small parts
Sponge filters, air stones and CO2 lines all need tubing, and it is worth using the right kind. Standard silicone airline is fine for air. CO2 requires CO2-proof tubing — ordinary airline is permeable enough that you will lose gas through the walls and wonder why your bubble count never matches your drop checker. We sell both, by the yard, and it is the cheapest problem on this page to avoid.
UV and specialty pumps
Pump-integrated UV sterilizers combine circulation with UV clarification in one unit, which is a tidy solution for a green-water outbreak in a tank without a sump. See our UV sterilizers for the standalone units and when they are worth running.
Not sure what your tank needs?
Tell us the tank dimensions, what filter you are running and whether you dose CO2, and we will tell you whether you have a flow problem or a different problem wearing a flow costume. Both the Convoy and Mid-City stores are happy to talk it through, and both test water for free while you are in.