hi everyone,just decided to clean out my pond filter today & couldn't believe the amount of pond life in there, there was blood worms,shrimps and other sorts of crustaceans.also living in the stainless steel waterfall was some kind of nymphs not sure what so iv'e posted a few pics if anyone can id thanks.
Welcome to the site, dave.moore.
DoDad is very close but I believe that is an aquatic mayfly nymph - genus Isonychia, perhaps. Some damselfly species also have triple nymphal tails, yet the three segments are usually flatter or not as delicately pointed and their heads are typically more bulbous and pronounced, like the head of an adult form dragon or damselfly. The photo is blurry however, so it could also be a discarded nymphal exoskeleton and not the nymph itself. They discard this nymphal shuck upon hatching into terrestrial adults. 
Dave
Mayflies are a great indicator of your pond's water quality. They have a strong sensitivity to chemical and environmental polution. They prefer cool well oxygenated water - that's why the nymphs hang out in your waterfall. If mayflies are present in the larval and nymphal stages in your pond, you surely have a healthy little ecosystem there, dave.moore.