clear for 4 years now cloudy for months ?

Hi all,

I always thought I had quite a green (wet) thumb - great clear water - rare
fatalities - great plant growth - hardly a drama in the 1st 4 years or so of
my tanks life...

but yes - got a bit slack in the last 12 months - not changing water as
often as I should...
a few weird pesky stringy weeds started to appear...
my plants were just hanging in there rather than growing healthily...
a few deaths... lost my 2 khuli's, and my last few neons... tank now only
has guppys - still breeding like rabbits though.
quite a number of snails...

so i decided to get it back to its old glory - went on a ruthless snail
cull - went back to regular weekly 20% water changes with 50% gravel
vacuuming. and voila - my tank went from a clear unmaintained junkyard to a
tidy clean CLOUDY exhibition. :-(

I was sticking to the old adage of regular water changes will cure 99% of
all tank problems - so have just been doing this for the last 2 months - but
to no avail - still cloudy.

HELP ????

I'm thinking my snails were eating all the decaying plants and now that they
are gone that is what is clouding the water ?
though there isnt really to much decaying plant material around... ???

I've been feeding the guppies every 2nd day - minimal amount of food.
Should I stop dosing CO2 ?
Should I stop fertilising after water changes ? (iron & potassium)
I bought 2 CAE's 5 days ago - they are going like champions... munch
munch...

HELP AGAIN ???
thanx.
Steve.