Notice - Pond help required.....

Am fairly new to looking after ponds.... Anyway, have a pond in our back garden. It's quite a small one (only holds around 110 litres of water) but enough for a small fountain, some pond plants and maybe (if I can get the environment right) a few small fish. But for now I'd just settle for a clean pond.....

The water is pea green.. Have tried Interpet Green Away & sludge buster for nearly a month now without any noticeable improvement - have set up my own DIY filter (a skippy up flow filter) which has been running 24/7 for about two weeks now and spiked it with plenty of good bacteria.

Have tested the water using test strips to check for nitrate/nitrite/ph level etc but everything seems within the levels stated for a healthy pond.

Have got several pond plants growing in an old washing up bowl ready to be put in the pond but I want ensure that the water is safe for them first. I put some in last year and they died within a few weeks.

Anyone got any advice as to what I can do to try and clean up the water a bit? Any help or advice would be very much appreciated.

TIA