Any invention tell if canister filter is on?

[Maximus297759]

I’ve been in aquariums 40 years always had this problem. Canister will stop million different reasons. So I never notice until water change if working. I have touch them or grab hose feel flow.
 

I was curious is anything rig up to have red green light on 24/7 unless flow stops? Has be flow because it could be powered on and not working.

[Tihshho]

For other applications I've seen flow indicators that use a paddle wheel inline with the output so you can visually confirm if you have flow. Issue is I'm not sure all of these are made with aquarium safe materials, let alone if they can handle the GPH of some larger pumps. When it comes to adding one of these to a canister, I could see these being yet another point of failure either restricting flow or completely clogging. These indicators probably won't hold up well with algae growth as the paddles will start to catch and then you're going to end up restricting flow due to that.

The best and easiest method is to aim your output in a way that you can see flow in the tank.

[Andy's Fish Den]

When I've had canister filters and now with a tank I have with a sump, I have the return outputs set so that they cause ripples on the water surface and I can tell by the ripples if the flow is slower than normal. 

[Mmiller2001]

Some tank controllers can monitor power usages and notify you if it stops.

[Streetwise]

An Apex Neptune could monitor water or power and send an alert based on various conditions. Pricey, but cheaper than a leak or property damage. My leak detection kit has provided nice peace-of-mind.

[Maximus297759]

I can’t see ripples from flow because I keep water level so high. I was thinking if used air tap on outflow under water ran little airline out water. I could get outflow blow bubbles. If doesn’t create a suction I could hook air line.
 

but pretty sure I use this tap under water line and run hose up with valve I can get spray some bubbles.