Can coral sand be used as a biological medium?
No, it will quickly compact down hard, preventing proper water flow.
What is the correct canister packing to operate an under-gravel filter?
If a reverse-flow under-gravel filter is in use, extra biological filtration is unnecessary within the canister and only mechanical media should be used.

How can canister maintenance be made less of a chore?
Maintenance is considerably easier if twin valves are fitted to both the inlet and outlet hoses. The syphon need not be broken when the canister is removed and the risk of water leakage is much reduced.
How can algae be discouraged from forming inside the hosing?
A useful tip is to exclude all light completely from the hosing by wrapping it in strips of thin black plastic, thereby depriving any algae of all light. In theory, the algae should not form at all.
Why has the impeller become noisy in its housing?
The impeller can become noisy for several reasons:
1) there is insufficient water flowing past it to lubricate its action
2) there is air trapped in the impeller housing
3) the impeller, or impeller housing is worn.
aoid very cheap canister failter models as construction materials tend to be inferior and they can become noisy in a short time. High quality, but more expensive filters are always good.
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