UV Sterilizers are great at getting rid of free algae. Personally (though pricey) I recommend Aqua Ultraviolet sterilizers (find a dealer on their website or order online ( www.WaterWorldonline.com pond supply...I live nearby and got mine there. They also sell them online and claim to have them for the cheapest $$$...)). What I like about them is they have a lifetime guarentee/warranty, very sturdy construction (its housing is also UV resistant so you won't have to replace it like you would with other brands), etc.
Another brand I have no experience with but is more affordable is Coralife's Turbotwist UV sterilizers.
HTH,
~Ed
Another brand I have no experience with but is more affordable is Coralife's Turbotwist UV sterilizers.
HTH,
~Ed