Guide · Tubing and check valves
3/16 in vs 4 mm airline tubing
Why 3/16 in and 4 mm airline are different sizes, which pumps and valves use each, what 'food grade' and the DEHP warning mean, and why all tubing hardens.
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Short answer
They are close but not the same. North American 3/16 in airline is about 4.76 mm; Fluval lists its air pump hose as 3/16 in / 4.78 mm.[1] European parts such as Tetra's CV4 check valve and EHEIM's air100 pump use 4 mm hose.[2][3] Match the tubing to your pump outlet and valve barbs, and expect any airline to harden over time.
Which gear uses which size
| Part | Stated size |
|---|---|
| Danner airline and check valves | Standard 3/16 in tubing; valves fit most common 3/16 in inside-diameter airline[4] |
| Fluval A101, A202, A402 air pumps | 3/16 in / 4.78 mm hose[1] |
| Tetra CV4 check valve | 4 mm internal diameter hose[2] |
| EHEIM air100 air pump | 4 mm suction-side hose[3] |
| Aquarium Co-Op black airline | 1/4 in; the page does not say inside or outside diameter[5] |
The size that matters for fit is the inside diameter, because the tubing slides over a barb on the pump, valve or air stone. A fraction of a millimeter makes the difference between a snug fit and one that slips off or leaks air. Mixing 3/16 in tubing with 4 mm fittings may work loosely or not at all, so keep a setup on one standard where you can.
"Food grade" and the DEHP warning
Aquarium Co-Op describes its black airline as food-grade PVC tubing and carries a California Proposition 65 warning for DEHP on the same page.[5] "Food grade" is the maker's term, not a finding about fish. We found no study that compares airline materials for fish safety, so we make no claim either way.
EPA describes DEHP as a phthalate most commonly used as a plasticizer, and released its final TSCA risk evaluation for it in December 2025.[6] That evaluation does not mention any aquarium tubing; it is context for what the warning refers to.
All airline hardens
Aquarium Co-Op says all airline tubing eventually hardens when left in water for long periods, and suggests cutting off 0.5-1 inch of hardened tubing before reattaching it.[5] Some packaging promises tubing that never gets brittle; treat that as marketing. Danner, for example, uses that wording, but the claim is not backed by any data we found.[4]
What to do:
- When tubing is stiff where it meets a barb, trim the end and refit it.
- When it cracks, or no longer grips, replace that run.
- Check tubing as part of routine maintenance; the maintenance checklist has a slot for it.
A standard 3/16 in roll
If your pump and valves are 3/16 in, a plain roll of standard airline covers most setups. The Penn-Plax roll below is sold under Penn-Plax's Amazon storefront. Its listing describes it as 3/16 in, 25 ft; we found no Penn-Plax maker page or part number for it, and the listing does not say whether 3/16 in is the inside diameter. Check the fit against your pump outlet and valve barbs.
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Questions
Is 3/16 inch airline the same as 4 mm?
No. 3/16 in is about 4.76 mm, and Fluval lists its A Series hose at 3/16 in / 4.78 mm, while Tetra's CV4 valve and EHEIM's air100 use 4 mm hose.[1][2][3]
Why does airline tubing get hard?
Aquarium Co-Op says all airline tubing eventually hardens when left in water for long periods, and suggests cutting off 0.5-1 inch of hardened tubing before reattaching it.[5]
Is 'food grade' airline safer for fish?
'Food grade' is the maker's term; we found no source that tests airline for fish safety. Aquarium Co-Op's food-grade airline also carries a California Prop 65 warning for DEHP.[5]
What is DEHP?
EPA describes DEHP as a phthalate most commonly used as a plasticizer. It released its final TSCA risk evaluation for DEHP in December 2025; that evaluation does not address any specific aquarium tube.[6]
Is 3/16 inch the inside or the outside diameter?
Danner states 3/16 in inside diameter for the airline its valves fit. Not every listing says which, so check the pump outlet and valve barb before you buy.[4]