hi there thanks for promp and helpful reponse ...
I believe it to be blanket weed mainly around the top of the pond and algae around bottom of pond. have a fairly good pump and uv light which i have tirned down and kept running over winter... however i dont think this is sufficent in summer as its an all in one pump and filter and i need to clean it every three days to keep the water half clear have a few more outputs for electric if needed.
Someone suggested adding grass carp as this would help with controlling the weed?
Only second year with the pond as this is the first winter all fish survived and look very healthy..
Sorry for this epistle, but it goes into detail so anyone reading it might care to get an cup of tea, or something stronger, before reading on.
last point first
Grass Carp !!!!!! Ouch.
When the blanket weed has gone (if they choose to eat that before attacking fresh young plant growth) they will destroy other plants in the pond. They are not a indigenous specie of this country and have become a pest on some waterways. Not the answer for a garden pond despite their availability in some retail outlets.
Back to UV lights, over time they lose effectiveness. The light still works but does not have the same effect as when new. The bulbs therefore need replacing before they stop working.
The other thing about a UV light is getting the correct flow of water through them.
Too fast and they dont kill off either the green water algae or any parasites which might attack the fish.
Too slow and the algae and the parasites can grow faster than the uv kills it off.
There is generally no need to leave a uv on over winter, consumes electricity to no usefull purpose.
As you enter winter, and come out of it, it is worth leaving it on to reduce the risk of parasitic infection brought on by the changes in temperature between warm days and cold nights.
I suspect the 'weed' you refer to at the bottom of the pond is probably also the onset of blanket weed.
It could of course be the inital re-growth of any oxygenating plant you put into the pond.
The risk of green water algae bloom can be reduced by giving the pond surface area some temporary cover from the sun until the natural balance created by this years growth of plants takes effect. Anything which floats without eventually sinking will achieve this.
Don't use it unless you have to, but if you get green water then do so until natural plant cover of the surface takes place.
There are numerous products on the market for both green water algae and blanket weed, however its worth trying one of the more 'organic' methods first.
Step one, remove as much blanket weed as you can by hand.
Step two, speak to wife/ girlfriend or whoever you know that wears tights or stockings (unless the pond is huge you only need one leg) and ask them for the next pair they ladder.
Step three, Loosely pack about half of one stocking leg with
Barley straw and tie the stocking in a knot just above the straw.
You dont need a full size bale of Barley Straw, a farm would probably be cheapest place to get enough to do the job, if not then a pet store should have mini bales.
Step four, Attach a piece of non rotting string to the top of the stocking leg
Step five, place stocking leg full of straw into pond, in a place that is accessible but not displeasing to the eye and attach the sting to something at the pond edge so that the stocking leg full of straw is retrievable. To help it soak up water quicker push it under the surface a few times.
Wait until straw sinks, this will take a few days. ( no I dont mean you have to wait by the pond til it sinks
)
Step six, once the straw has sunk, lift it back out the pond on a weekly or 2 weekly basis throughout the summer and shake it well. This is to keep introducing oxygen into the straw.
Step seven, once straw is almost disintegrated, cut open the stocking or tights leg, dump any remaining straw on the compost heap and refer to step 2 onwards
If step seven hasn't happened before winter sets in, remove it anyway and refer to step 2 onwards if you need to next year.
The above is the cheapest method to use Barley Straw, alternatively go to a specialist water garden outlet and pay through the nose for a couple of peanut bags full of their magic blanket weed barley straw that will last a couple of months. (Its not magic, its the same stuff you get from the farmer)
I hope all this is of some help