NewGardener wrote:
Hi, this issue is driving me a little nuts and as i do not have green
fingers I have joined this group and hopefully have posted in the right
forum.

The previous owners of our house laid down an area of hardcore (stones,
earth, around 10mx10m) and over time some grass, weeds, earth have
accumulated. From our first year we have had this algae/seaweed
'growing' on top of the area. It has a slimy texture, green, cresent
shaped nodules growing in bunches that join to form mats over the whole
area. None of our neighbours have it with similar terrain/drainage
issues.

I think a picture might be worth a thousand words here.

Some of the sedums a few of which are rather invasive sort of fit your
description. They tend to thrive on well drained areas and hardcore but
will also block gutters. I can't think of one with cresent shaped leaf
nodules most are oval or egg shaped. They grow as mats with a thin stem
and small fat leaves. They flower and spread by seed.

It does not grow on the 'grassed' areas but on mud, mosses, stone
areas.

We usually scrap it up in shovels (unfortunately the hardcore is porous
and difficult to brush/scrap) and we have thought about putting down
bleach. Bleach certainly kills it but obviously not a good solution,
but no water course near to us. Also we would prefer a solution that
inhibits regrowth.

Firstly: What is it? And what can we do to get rid of it?

If there is no risk of runoff then sodium chlorate is as good as
anything for a quick weedkill on a hardcore path.

Regards,
Martin Brown