An annoying problem! MP40

JD117 · Jan 26, 2026

Hey reefers, as you can see from the photo I’ve ran into a slightly unfortunate problem where the MP40 perfectly fits when I have the gasket on, but not when the spacer is on.

Ideally I wanted it on that side of the tank as I’ve replaced my old wave maker with this and have setup my tank in a way that has the lps and softies in the slower area of the tank. It’s currently on the other side, but that means the flow is now opposite to what it used to be. It is almost much more aesthetic that side where you can’t see the huge power unit.

Long story short - is it possible to use the gasket instead of the thin spacer

Glass thickness is 1.1-2m (just below recommended minimum)

I appreciate the manufacturer has recommended that for a reason, and I’m no specialist in weight / pressure distribution on glass, but how serious is this issue?

Thank You in advance!

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TX_REEF · Jan 26, 2026

It should be fine, the magnet isn't powerful enough to crush glass as far as I know. I'm thinking you may get some vibration noise with the pump against the wall, though.

JD117 · Jan 26, 2026

TX_REEF said:
It should be fine, the magnet isn't powerful enough to crush glass as far as I know. I'm thinking you may get some vibration noise with the pump against the wall, though.

That’s what I’m hoping (for the crushing of glass) as it doesn’t seem incredibly strong

Regarding the wall I have <1mm clearance so it isn’t touching it but dang near close haha!

exnisstech · Jan 26, 2026

I guess I don't really understand the question. Why do you not want to use the recommended spacer? I have MP40s on 3/4" glass with just the gasket and no spacer. I also have them on 10mm glass using the thin plastic spacer.

EDIT: its not going to crush the glass. I think the distance between the two units needs to be a certain amount for the unit's to function properly. I don't think clamping force is the reason for the different spacers. Speculation on my part. I ran mine with just the gasket and no spacer on my tank with 10mm glass but they are quieter without the spacer installed.