Pond pump speed control

In uk.d-i-y Tim Downie wrote:
Is is possible to use a speed controller (like a light dimmer) with a small
pond pump?

I have a Bermuda 3000 (3000l/hr) submersible pump that's really a bit more
powerful than I need. The motor has a solid rotor that appears to be made
of a ferrite like material.

I know that speed controllers can cause overheating problems with some
motors but given that it's underwater with water bathing the rotor, I don't
imagine this would be a problem in this case.

In this case, simple speed controllers won't actually work, it'll stay at
a constant speed (3000RPM) until it stops working, and hums loudly.
Suitable speed controllers are going for around 40-50 quid on ebay.
Search on
inverter phase motor induction
on ebay, searching titles and descriptions.