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I am attempting to build a photobioreactor, in other words a water-filled system for growing algae. I'm using a series of 1.5" clear tubes to hold the water, the bottoms of which will connect to a PVC manifold I've assembled by gluing a bunch of tees together. The nominal pipe/fitting size I'm using is 1-1/4" schedule 40 PVC.

There are ten tubes (currently) and I need to be able to bubble air through each tube to deliver carbon dioxide to the algae. I don't know how to run the air tubing into the manifold underneath each tee to deliver the air bubbles. The tubing and fittings I'm using for air are actually 1/4" drip irrigation parts.

I'm attaching some photos of what I have tried so far:

First attempt: drilled 1/4" holes, pushed tubing in, silicone around each hole. Result: leaks manifold, first attempt

Second attempt: Enlarged holes slightly (5/16"), siliconed the "misting" drip irrigation fitting right to the hole. Result: came apart during handling. second attempt A second attempt B

My next attempt was going to involve enlarging the hole and tapping 1/4" NPT threads into the wall of the fitting, and screwing a barbed adapter directly in. The reason I didn't do this from the beginning is because of the cumulative cost of all the extra fittings. I'm looking for other suggestions or perhaps some part or fitting I've not heard of that will make this easier.

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    Can you run an irrigation tube inside the bottom of the manifold and then just put a pierced connector under each tee? Exit the tube at one spot with a glued in rigid elbow. – bib Jul 21 '15 at 11:21
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Assuming you have or can get the clear tubes to attach and not leak, I'd suggest a 1-1/4" (or reducer and 1/2") PVC pipe parallel to your clear pipes, running above water level, and NO penetration for the CO2 feed line; not only run it in the bottom of the pipe as suggested by @bib, but run it inside regular, normally solvent-welded PVC vertically as well, all the way above waterline. No funky or fragile seals between plastics that don't solvent-weld nicely.

From fishtank experience I'd also suggest that you be open to running 10 tubes so that you can balance the airflow if it does not opt to cooperate and divide evenly in practice (one of those things where things are the same in theory, but often different in practice).

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