My weir

[wvned]

Is slowly passing less and less water. I have a PVC plank casting a shadow on it. Nothing but a tiny bit of brown algae is on it. I scrub it with a toothbrush when needed. But the Vortechs are producing a wave that is throwing water out of the tank and making a large puddle in front of it. MP60s running nutrient transport mode.

My overflow rear box has had the water level dropping. The front box was low too. The drains that used to be adjusted to maintain the level are now too fast and draining the box, Yesterday we cleaned up the puddle and I turned down both return pumps to 70%.
It's been fine for years until now. Then the water level slowly got too high in the tank.

Today I took a spiral cutter in my Dremel and opened and deepened the slots in the weir. Then I turned the pumps back up to 90% like I used to run them. I adjusted the gate valves and made all the levels correct so it is quiet again.

This makes no sense to me. How can flow through a weir change with. nothing growing on it?

 

[kharmaguru]

This makes no sense to me. How can flow through a weir change with. nothing growing on it?

Swelling of the material? Assuming it's some form of plastic.

 

[wvned]

Swelling of the material? Assuming it's some form of plastic.

It is a regular glue on overflow box I had made because it had to be deeper than off the shelf ones. I am not sure what it is actually constructed of. It was made by Modular Marine.
It had to go down into the tank more because of the size of the bulkheads that hold the rear box on. I installed it with regular aquarium silicone.
It had narrow slots so I cut out every other one a year and a half ago. Now I have deepened them.
I would think this was a stay the same forever thing.

 

[griss]

This is very interesting, I've never heard of this happening before. I believe Modular Marine uses acrylic so, I can't imagine the material changing is size or swelling as Sean mentioned but, who knows???

 

[SantaMonica]

Something stuck in the pipe?

 

[wvned]

It was fine man months. Then I started turning the return pumps down.
I cut every other bar out between the slots.
It was fine a year and a half then I started turning the return pumps down. 70% is just too low,
Spral cutter (like a Rotozip uses) used to deepen the slots.
Not the kind of thing I have ever had to worry about before. I am still adjusting it

Something stuck in the pipe?

The drains are sucking the overflow box level down because less waters coming through the weir in the front.
My next option would be to have a bigger one made and install it.

 

[SantaMonica]

Maybe set up a temporary siphon pipe over the side and see if it's fixed.