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[APD] Re: How do I avoid bubbles in siphons?

Rod wrote:
A couple of days ago I setup my dream system.  It uses
two 20 gallon high tanks as bio-remediation for a 120
gallon planted tank.

Water is pumped via a Fluval Stage 4 from the 120
gallon tank into a 15 watt UV steralizer (I have had
problems over the years with fish tuberculosis) and
from there goes into the top 20 gallon tank, an algae
tank with 72 watts of compact flourescents on 24 hours
a day.

>From there it flows into the second 20 gallon tank,
also 72 watts of compact flourescents (from AHS, great
people to work with), lights on 12 hours a day,
opposite schedule from the main tank.  This tank is
heavily planted with Vallisneria species.

Finally it flows back into main tank.  This is lit
by 12 48 inch t8s, currently 10.5 hours per day.
Other than the trip thru the steralizer all these
flows are by gravity via 1.25 inch ID tubes.

My problem is that there is pearling going on in these
tanks 24 hours a day somewhere and the siphons are
getting bubbles in them which tend to collect at the
highest point, with disatrous consequences if left
untreated.  I need a system that can go without
maintenance a minimum of three weeks, and this is not
going to make it.

I tried putting 90 degree U curves in the bottom of
the siphons so that rising bubbles would not enter
and this was surprizingly uneffective.  With all the
oxygen plus co2 in the water I'm not sure what these
bubbles are, but they may even be rising spontaneously
inside the tubing.

Does anybody have a suggestion for keeping these
siphons flowing?


That sounds like quite a setup, a lot like a reef algae filter with the 20
gallon tanks on opposite light schedules .

You could do as Scott H. suggested and increase the flow rate thru the
siphon tubes. I will assume you have the clear plastic "U" types. A high
enough flow rate will clear the siphon tubes of any bubbles.

Another method reefers use is to plumb a check valve in at the very top of
the siphon tube using silicone or acrylic cement, so the valve is sticking
straight up from the bend, with the flow direction exiting the check valve
from the tube. You then use a small (Rio 600 possible) powerhead placed in
each of the 20s that has an air atttachment and connect the check valve to
the powerhead. The powerhead draws the accumulated air bubbles and a bit of
water thru the check valve continuously and keeps it clear. If you can find
a powerhead with adjustable flow in addition to an airline attachment point
all the better. It wouldn't take much pull to keep it clear. You might be
able to do both siphon tubes with one powerhead if you controlled and
balanced the suction with a 2 way gang valve.


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