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Re: replacing Eheim tube

Cavan asked about tubing to replace his Ehiem siphon:

> If the tube isn't exactly the same, can it strain the
> filter somehow?  (That may be a stupid question.)

The only problem would be if the diameter was significantly
smaller, or the tubing significantly longer or involved a
lot more joints.  In those cases, the water flow is more
restricted.  If the flow is too low to feed the pump
adequately, then you can create cavitation at the impeller,
which isn't necessarily bad unless there is a lot of it.  I
think you would have to go pretty far to hurt the pump.  So
long as the impeller stays in-water, it should be pretty
doggone tolerant of water flow rates.
> One other question:  Do I have to use the stuff called
> CPVC?  I guess I don't want plasticizers in the tank! 
>  I saw something in the archives about this but I'm
> still not sure what is and what isn't safe to put into
> the tank.  

You certainly don't have to use CPVC -- Chlorinated
Polyvinyl Chloride pipe is basically PVC with added
chlorine to handle higher temperatures. [I have no idea how
that works.]  CPVC's primary advantage is that ith
withstands heat resists some corrosives better than plain
PVC.  So it's used with hot water and corrosive liquids. 
But were not talking about the kind of heat or corrosives
that you will have in an aquarium.  So it should not be a
concern re you aquaria ;-)

CPVC is generally more expensive than plain PVC.  Often it
is grey or dark colored while the plain PVC is white.  This
makes it easier on the construction job to tell which is
which.  But you can find PVC in grey, dark grey, white,
transparent.  It's easily worked.  CVPC *and* PVC are used
for household water supplies and drains in states where the
fire code does not prohibit it -- it's plastic and it gives
off toxic fumes when it burns.  In terms of potability,
CPVC and PVC are both fine.  If any plastisizers leach from
the plastic, *which happens with virtually all plastics
over time*, the rate is so slow that it should not be an
issue.  Maybe if you kept the same water for years and
years and years, but even then it is doubtful you would be
to distingusih any effects.

Other choices are polyethylene and polypropylene. They both
have more than adequate properties for aquaria use. 
Polyethylene is generally a soft, ductile material.  Look
on the bottom of a plastic bottle where the recycle logo is
-- many of them are marked "HDPE" for "high density
polyenthylene."  Some are marked LDPE; guess why ;-) 
Polypropylene is softer than most PVC pipe and resists
corrosives well.  It's used for drains and lawn sprinklers.
 Lots of plastic bottles are polypropylene.

There are other materials, all of which will cost more and
provide little benefit in an aquarium set up.

Oh yeah, there is also ABS
(Acrylonitrile-Butadiene-Styrene), which is usually black. 
It's usually a plastic foam (really a foam center with a
solid skin inside and out and melted edges.  But solid-wall
versions can be had for a price.  The foam version is
lighter and has less strength than PVC for a given size but
would me more than adequate for aquaria use.  It's more
often used for drains than for water supplies, mainly
because of the strength/size issues and cost.

And of course, soft vinyl tubing is always an option. :-)

Hope that helps,
Scott H.

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