Re: pond

[Thomas Barr <tcbiii at earthlink_net>]

> I'm in the UK, Devon, and  had a 5000 gals garden pond constructed about Sept

You may consider using pots and soil capped with gravel for the plants.
 
> The calicum is high in the water, appears on the leaves of the pond weed & the
> pH is also high.

What plant is "pond weed"?. Egeria? Hornwort? Hydrillia? Potamogeton?
This is normal.

>  I've logged it every 15 mins & follows normal diurnal cycle
> but start in the 7's and rises to high 8's in the afternoon.  Tried to lower
> pH by adding peat (about 100 litres so far) but effect is very
> temporary...possibly water is too well buffered.

This is not going to help you.
Big swings in small closed pools and ponds are simply part of nature.
Some pools near here go through pH of 6 to pH of 10. Salt water Tide pools
go from 8.1 to over 10. What your seeing is common and natural. Seeking to
control nature and pH at this scale is fruitless in my opinion.

> Is anyone aware of a way to remove / precipitate out the calcium from the
> water? 

Commercial water softeners, RO water, acids and acid rain etc. Not
economical for a large pond.

> Also how do I effectivly reduce the pH without having to add bale upon
> bale of peat?

CO2 but that would involve a huge CO2 system.

>  Also, anyone aware of a natual predator of B.weed that won't
> eat my other plants...or a way of getting rid of it? (tried barley straw,
> bacteria to consume nutrients etc...pH probably too high?!).

Blanket weed? An algae? Looks like green hair? Does it grow only on the
bottom of the pond?

Straw is good for green water, but I'm not sure the Green water looks worse
than rooting straw in one's pond.

It'll have no noticeable effect on attached algae from what the research has
shown and what I've seen in aquariums.

I think a few things might help you out here.
Stop worrying about the pH swing. It's going to happen and there's not much
you can do at this large size.
Realize ponds go through seasons, sometimes they have algae, algae is a
natural part of the cycle.

Add more plants. This is typically the best defense for a pond. Adding many
plants reduces nutrients a great deal. Floating plants in particular are
great. They are unconcerned about the pH and get plenty of light.
They block the light to the algae below also. They tend to grow fast.
I've added Sag's, Hyacinth is good, water lettuce, hydrillia, Elodea,
hornwort anything cheap and available near the start of summer.

 Adding these near the early-mid summer phase each year will yield decent
results as it will greatly reduce algae presence. Remove excess growth
occasionally. You might have to remove some algae here and there but it
should not be that much. Keep the pond fairly full of plants. I'd get rid of
the stickle backs and add larger fish that don't eat all the algae eating
herbivores that are smaller zooplankton like Daphnia and insect larvae.
Smaller pond snails are good also.

More plants when you need them, get large fish that will not the herbivores,
try a few different plants, use pots for adding nutrients to your rooted
plants.
See water lily sites for more info.

Regards,
Tom Barr