Aquarium Heater & Filter Buying Guide
The right size filter and heater make far more difference to a healthy tank than the specific brand you choose. This guide covers how to size both correctly, compares the main types available, and gives a quick reference table by tank size.
1. Why Sizing Matters More Than Brand
An undersized filter or heater is one of the most common reasons a new tank struggles — not because the equipment is faulty, but because it was never matched to the tank in the first place. Getting the size right matters far more than which brand you choose.
2. Sizing a Filter
Aim for your filter to turn over the tank's full water volume roughly 4 to 6 times per hour. A 100 litre tank, for example, needs a filter rated at least 400–600 litres per hour. Heavily stocked tanks, messy eaters, or larger fish benefit from sizing toward the higher end of that range.
3. Sizing a Heater
A common starting point is roughly 1 watt per litre of water, increased for cold rooms, draughty spots, or a big difference between room and target tank temperature. Two smaller heaters rather than one large one can also add redundancy — if one fails, the tank does not crash in temperature.
4. Filter Types Compared
Type | Best For | Trade-offs
Internal filter | Small/medium tanks | Takes up in-tank space
Hang-on-back (HOB) | Medium tanks | Some water noise
Canister filter | Larger, heavier stocking | Higher cost, more involved to clean
Sponge filter | Fry, shrimp, hospital tanks | Limited for large fish loads
5. Heater Types Compared
Type | Best For | Trade-offs
Submersible glass | Most common, budget | Fragile if knocked
Submersible shatterproof | Boisterous/large fish | Higher cost
In-line (canister) | Larger, established setups | Adds plumbing complexity
6. Quick Sizing Reference by Tank Size
Tank Size | Filter Flow Rate | Heater Wattage
40–60 litres | 160–360 L/h | 50–100W
60–100 litres | 240–600 L/h | 100–150W
100–150 litres | 400–900 L/h | 150–200W
150–200+ litres | 600–1200 L/h | 200–300W (or two units)
7. Common Buying Mistakes
● Buying to match tank size on the box rather than actual litres and stocking level.
● Choosing the cheapest heater with no guard for a tank with large or boisterous fish.
● Underestimating room conditions — a draughty garage needs more heating power than a warm living room.
● Ignoring flow rate on planted or shrimp tanks, where excessive flow can stress delicate species.
8. Frequently Asked Questions
Can I use a filter rated for a bigger tank than I have?
Generally yes, and it gives you margin as stocking grows — just check flow is not too strong for smaller or delicate fish.
Do I need a heater in a warm climate?
Often still yes — indoor temperatures can drop more than expected overnight or in air-conditioned rooms.
How do I know if my filter is undersized?
Persistent cloudiness, elevated ammonia or nitrite despite water changes, and visible debris are common signs.
Should I ask staff for sizing help?
Yes — bring your exact tank dimensions and stocking plans in-store for a specific recommendation.
