Making Water Flow

This morning when I came into work, I noticed that our feeder goldfish tanks weren't looking quite right.
Well...considering they're all empty right now...that's definitely not right.
But I noticed that each tank seemed to have a different level of water, when usually they're all at the same level.

I hadn't thought much more on it though, since it's common for the locklines (that bring water into the tanks) to get clogged up (like with snails cus those things are everywhere) and so I figured that the locklines in those tanks had clogged after a coworker had gone through and gravel vacuumed the tanks to keep them looking nice. Which meant that the water levels had remained lower.

However, later, once the lights to the fish tanks had turned on when the store officially opened for the day, I noticed that it wasn't just one or two tanks that weren't flowing in the feeder goldfish section. ALL of them weren't flowing. 
O.o 
Now that's just...weird.

Could they all be clogged?
I twisted off one lockline to see if there were any debris trapped behind it...but no water whatsoever flowed. 

That was...concerning.
But I halfway figured that the cause was probably due to an issue in the back behind the fish wall.
As the goldfish tanks run on a different water system from the rest of the fish wall. And that water system, doesn't replenish it's water in the sump (holding tank) in the back that filters the water. So if the water levels in that back holding tank get too low...no water can flow into the goldfish tanks up front.

A check in the back proved this theory to be correct.
The sump was nearly empty.
Which meant that whoever had gravel vacuumed the tanks recently...had done quite the thorough job. As usually a quick sweep through the tanks doesn't affect the flow that much.

Thankfully.
Fixing it was a simple thing.
Which involved adding more water into the sump in back so that water could flow into the tanks up front.
But because I was adding in a ton of water, that meant I then had to go out and clear out all the locklines to ensure that no debris were constricting the water flow. 

Luckily its all flowing smoothly now. 
And thankfully...we had no goldfish in those tanks when this happened.
because I probably would have come into a ton of dead fish this morning if we did. *shakes head*

-Sarnic Dirchi