ime asking this question when i think i kind of already know the answer, just want a different perspective on it, lets rewind back 3 years, i was cleaning out the pond and in amoungst some plant pot gravel i found a big red leech thaught it must be the only one, prob came on a plant, disposed of it (took it to the local marsh land) never thaught anything about it, now i havent cleaned the pond out since then, over the last few weeks i took some tadpoles (2) from the pons and i am keeping them in a tank in the kitchen and my 6 year old son ethan is keeping a diary of how they change and grow legs etc ! yesterday i took some stones from the pond to put in the tank just to give the tadpoles somewhere ti hide and investigate and swim round etc, when i checked on them this morning i discovered a small leech squirming across the side of the tank, so these leeches must have been in my pond for atleast the last 3 years ! ive never had a problem with any of the fish, can anyone think of a genuine reason why these leeches might be a cause for concern or should i just forget about them ?