It causes extreme frame rate drops.

Tanks and Channels are now hybrid TESR-ISBRH's, the water is rendered as TESR and the rest as an ISBRH (InfinityRaider@0fd5f34).
Fluid levels are now synced with a seperate packet. Now there will no longer be block updates when the discrete fluid level changes.

What version?

1.4.0-alpha

I must have fucked something up then, I changed it to reduce the number of block updates, I'll investigate.
Is it worse than in 1.3?

Not sure. The issue gets serious when you have a lot of crops and tank in the same view chunk (16x16x16).

I have code that turns the tanks and channels into hybrid TESR/ISRBH where the water is a TESR, the registering is commented out because i can't get the water to render correctly, but I can add a config option to enable it anyways.

I can confirm this. Having a network of irrigation channels with sprinklers (and one tank to provide everything with water) in a 32x32 area causes a ca. 10 FPS drop.

the network consists of 15 sprinklers, 96 irrigation channels and one tank.

I'll rewrite irrigation systems when I find some time, because they were written at a time when I was new to modding, and it received a few patches, but its still a monster.