Question
QUESTION: Im just getting rid of the hideous blanket weed & amongst it I found small dark red worms or are they leeches?.. They seem to 'stick' to any surface.. also tiny prawns. Are they both OK to leave in pond. Its a 6foot circular approx 250galls UK. 18inches deep with a mix of orfe & goldish..No Koi. I have a UV filter & small fountain

ANSWER: They may actually be red worms, or they could be midges.  I can't tell you what the prawn-like creatures are for sure.  Neither of them is inherently bad for a pond, but with a pond of 250 gallons, you way want to remove the majority of them so that they don't overwhelm the water feature.

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QUESTION: Also as Im removing as much blanket weed by hand what product do you BEST suggest to add to remove the rest. I tried the barley last yr & it made a horrible mess & the barley+ sachets just didnt seem to do the job. Thank u for your quick response to 1st ?

Answer
The key is to remove as much of it as you can by hand.  Dying algae releases toxins into the water so you need to get the browning algae out as best you can.  Try using the barley-concentrate liquid as it causes no mess.  Also, it's nearly impossible to remove the last 1/4 cm of algae/sludge from the liner and rocks.  The plus side is that it actually helps the pond, so the only incentive to remove it is for aesthetics.  I'm sorry I couldn't help more to identify the critters.