I need you guys to check my logic on this. It seems so
clear to me, but I ran it past the guys at the pool supply
store, and got nothing but blank stares.
A friend has a fiberglass pool. It's seven years old, and
he's never changed the water, not even a little. And since
he uses stabilized cholorine, there's no telling what the
stabilizer has built up to. He lost about six weeks of
swimming time last year trying to get the algae under
But he has been warned never to drain the pool more than a
foot or so because of the water table level - it will pop up
out of the ground just like a boat, which would be a
I think it should be relatively easy to change out
essentially all the old water with new, and to do so
without dropping the water level in the pool at all, and
without wasting any water. All you need is a membrane that
separates the old water from the new.
So you go to Home Depot and buy a roll of 0.35 mil plastic
sheeting (12'x400') for $24, and some shipping tape, and you
tape together what looks like it might be a liner for the
pool, or at least that big - doesn't have to be exact, just
not too small in any dimension. Then you turn off the pump,
anchor the edges of this liner around the edge of the pool
deck with a few bricks, and pile all the excess out onto the
pool surface. You want to do this on a calm day.
You set up maybe four or five garden hoses as siphons that
suck water out from under the liner, and start them draining
the pool. You put maybe two garden hoses as supply hoses on
top of the liner, and over time adjust one spiggot so the
inflow rate is about the same as the outflow, so the water
level stays constant.
Over a day or two, the liner will slowly expand as the new
water comes in and the old water goes out, and will fill out
to conform more or less to the bottom and sides of the pool.
It doesn't have to have any strength at all - all the forces
on it will be applied very very slowly and gently, and it
will never have to actually "hold" water. It's just a
diaphanous membrane that always stays at the boundary
between the new water and the old.
When it's done, turn everything off, gently remove the
sheeting liner, turn on the pump, superchlorinate, and
If you want to get fancy, you can run one of the fill hoses
through an auto-fill gizmo. Then you don't even have to
check on the fill rate - the water level will be
I think this will work. Is there a problem with it, or
something I haven't considered? Whadayathink?
I would appreciate any comments.