Is it safe to use a ball valve to reduce the water flow that much it still is coming out quite fast even tho it’s pumping a meter up into the tankSorry, not sure about one that could control to the second. The pump may be 280l/hour, but there will be head loss since I assume you're pumping it up from inside or next to the stand. It would be best to get a gallon jug and see how long it takes to fill it up at the same level as the top of your aquarium.
Maybe you could use a ball valve to slow down the flow? This should allow you to set a timer to minutes and not seconds.
The only issue I can foresee is some ATOs have a built in redundancy that won't let the pump run longer than X amount of time. If you slow the flow down, it's possible you could trigger that fail safe. That is assuming your ATO even has that feature. Also I would put the valve inside your reservoir, just in case it ever leaked.
My pump will only do that after the first fill so won’t be an issue when on a timer. I was jsut making sure it so wasnt gonna ruin the pump by restricting flow
Generally not an issue to restrict an AC pump on the output, as long as it's not excessive. You can always use a T fitting to circulate the water back into the reservoir. That would relieve any back pressure and slow down the flow.
