Most likely it's the trace elements that your water provides. No way to get
rid of those (yet).

Sam

"Conrad" wrote in message
...
Hello

I have to occassionally top up my pond (2500 gallons when full) - not,
I hope, due to leaks but evaporation - yes, we do sometimes get hot
weather in the UK.

Anyway when I top up the pond I always get a "green water " problem
shortly afterwards. I use tap water as I do not trust run-off rain
water from the various downpipes in case there is some chemical
contamination from the roof materials. I'm pretty sure it is the
nitrates in the water that's causing the green water in the pond and
would like to find a way to treat and store top-up water.

I have thought about dumping a load of algae/blanket weed in the water
in the hope it will use up the available "food", die off and leave the
water more suitable for topping up the pond.

Has anyone any ideas on this or can suggest some other way to treat
the water, preferably not with chemicals but if it's the only way I'll
give it try.

Thanks in advance for any help.

Conrad