Fluid pipes misbehaving

That middle section has 2 possible directions to go - Electrolyzer and farm tile. You also have 2 pumps pumping water. So the water in the middle doesn't know where to go. Since it already passed the electrolyzer from the point of view of the left pipe, it "thinks" it's traveling towards the hydroponic farm. Try cutting the pipe between the electrolyzer and the left pump and it works - that way you have only 1 source and 2 destinations.

 

Another solution would be to put a bridge between the 2 outputs that shows in which direction the water must flow:

Now the left pump will only supply the electrolyzer, the right pump will supply both.

Ohh!  So it is confused because I left the old pump connected, but just offline?  I was using the left water originally then switched once I got the water sieve.  I thought the water would just flow into any pipe section that doesn't already have any.