The only creatures who desire a crystal clear pond are Humans and Herons! Humans spend an excessive amount of money trying to achieve this " unatural " state in still water just so the Heron can take advantage of the situation forcing the fishless pond owner back to the aquatic centre to restock again and again.
If what you desire is a natural / wildlife pond for frogs toads dragonflys somewhere for the birds to drink and bathe you dont need any filter or pump of any kind. The alge is an important part of the pond eco system. this "soup" works like plankton in the oceans. it feeds the little bugs that feed the bigger bugs that feed the frogs and so on
larger natural ponds can tolorate a few fish but they are not needed from a wildlife point of view. They are best avoided in small ponds. they do not " cause" alge directly , this is caused by sunlight and increased levels of nitrogen. It is fish poo that it the usual culprit for increased nitrogen in small ponds.
the best way of keeping alge to a reasonable level is to have plants that cut out some of the light to the water, like lillies BUT these are really expensive and will quickly overfill a small pond, there are miniture versions but you could try water hawthorn which works in a similar way,
If you want frogs in your pond find someone who has tadpoles. they should be hatching NOW. frogs and toads will always try to return to the water they grew up in, so putting tadpoles in your pond is a better way to ensure a continued frog population than catching a passing frog and hoping that it likes whats on offer.
Herons do eat frogs as do grass snakes But that is the natural order of things and all the time there are plenty of crystal clear ponds with nice brightly coloured fish to eat, why bother with a frog?
pond snails are both male ansd female but there still needs to be two of them cos they need to" swap genes" but snail eggs often come in on water plants so that even if you dont buy them they will probably appear - bit like slugs, you get them regardless!
