These are the pumps used in R&R modules. They used to have brass gears when they were made in France, but with production moved to China the gears are now plastic (meh!). They still work okay in aspirated tanks where they don't need to push against much pressure. Kavan pumps have brass gears, but they're much bigger and more expensive, although well worth it if you have the space.
Alternatives, fit two unidirectional pumps one to pump in, one to pump out. Use a peristaltic pump- you can find printable versions on thingiverse. They tend to be slow at pumping compared to geared pumps, but a Holland has a low freeboard.
Alternatives, fit two unidirectional pumps one to pump in, one to pump out. Use a peristaltic pump- you can find printable versions on thingiverse. They tend to be slow at pumping compared to geared pumps, but a Holland has a low freeboard.
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