Charles Austen HL-BT Series
Charles Austen HL-BT Internal Aquarium Filters
Four compact power filters from 200 to 1,000 litres per hour
The HL-BT range is a straightforward family of internal filters for aquariums, nutrient reservoirs and small water features. The HL-BT200, HL-BT400, HL-BT700 and HL-BT1000 provide published maximum flows of 200, 380, 690 and 1,000 litres per hour.
The range also publishes maximum head figures from 0.65 m to 1.95 m. Head is useful when the outlet needs to lift water, but it should not be mistaken for the flow you will receive at that height. Flow falls as lift and resistance increase.
For ordinary aquarium filtration, livestock and media capacity matter just as much as pump performance. Choose a model that can circulate the tank without turning it into a washing machine.
Compare the four HL-BT models
HL-BT200: 200 l/h, 0.65 m maximum head and 3 W. HL-BT400: 380 l/h, 0.9 m and 7 W. HL-BT700: 690 l/h, 1.25 m and 10 W. HL-BT1000: 1,000 l/h, 1.95 m and 17 W. These figures are useful for comparison, but real flow depends on the outlet arrangement and how clean the media is.
For a gently stocked small aquarium, the lower models may be neater. Larger or more heavily fed tanks normally need the media and circulation capacity of the upper end.
Flow should suit the fish, not just the tank
Active fish may appreciate brisk circulation, while long-finned, juvenile or slow-moving species may need a gentler return. Diffuse the outlet across the surface or decoration rather than forcing a narrow jet straight across the aquarium.
If the filter is being used in a hydroponic reservoir or compact feature, check the required lift. A maximum-head figure is the point at which useful flow approaches zero, not a promise of full output at that height.
Routine care
Disconnect the filter before maintenance. Clear the intake, rinse mechanical media as needed and preserve established biological media. A steady decline in outlet flow usually means the intake or media needs attention rather than that the motor has suddenly become too small.
Reassemble seals and covers carefully and make sure the unit is fully installed in accordance with the instructions before power is restored.
Our recommendation
Do not size an internal filter to the bare aquarium volume. Tell us what lives in the tank and how heavily it is fed. A modest aquarium with messy fish may need more filtration than a larger, lightly stocked display.
Useful Related Categories
If you are planning the complete installation, these sections are usually the most useful next step: All aquarium accessories · MV internal filters · Air pumps · Air stones and diffusers.
Frequently Asked Questions
What is the flow of the HL-BT200?
Its published maximum flow is 200 l/h, with a maximum head of 0.65 m and a rated input of 3 W.
What is the flow of the HL-BT400?
Its published maximum flow is 380 l/h, with a maximum head of 0.9 m and a rated input of 7 W.
What is the flow of the HL-BT700?
Its published maximum flow is 690 l/h, with a maximum head of 1.25 m and a rated input of 10 W.
What is the flow of the HL-BT1000?
Its published maximum flow is 1,000 l/h, with a maximum head of 1.95 m and a rated input of 17 W.
Does maximum head mean full flow at that height?
No. Maximum head is the shut-off end of the curve; delivered flow reduces as lift and system resistance increase.
Which HL-BT filter should I buy?
Choose from aquarium volume, fish load, desired circulation and maintenance margin rather than using volume alone.
Can the outlet be aimed at the surface?
Yes, and gentle surface movement is useful for gas exchange. Avoid a strong jet that stresses the fish.
Can HL-BT filters be used in hydroponics?
They can suit small nutrient reservoirs where the materials, flow and installation meet the system requirements.
How often should the filter be cleaned?
Clean it when debris accumulates or flow falls. Heavily stocked tanks will normally need more frequent attention.
Should biological media be replaced regularly?
Not routinely all at once. Preserve mature biological media unless it is damaged or the manufacturer specifically instructs replacement.
Can I run the filter out of water?
No. Use it only in the installation position and water conditions stated by the manufacturer.
Can one filter provide enough oxygen?
Surface movement helps, but warm or heavily stocked aquariums may still require separate aeration.
Can the HL-BT1000 be too powerful?
Yes. A 1,000 l/h jet can be excessive in a small or gently stocked aquarium unless the flow is spread appropriately.
Do I turn it off for feeding?
Normally leave filtration running. If a particular feeding method requires a short pause, remember to restore power immediately.
Can you help select a model?
Yes. Send us the aquarium volume, livestock and desired flow and we will help compare the four models.
