@fragileassassin
Nice little RDWC build. I thought I'd share a few cents if that's ok...
I'd suggest "DC water pumps" in the future. I know you're not looking to buy something new right now mabye but when you do, get a DC pump, for example the "Jebao" brand (amazon, reef supplies). They consume less power, therefore adding less heat to the water, they're speed controllable, they have soft start (ramps up), they have a pause button (perfect for doing some quick maintenance).
Also, is the water pump you're using oriented vertically? With the input/output running vertically - up and down, not horizontally? That's probably causing cavitation (I think), as well as what someone already mentioned about having certain diameter restrictions before the pump intake could be doing that as well.
I don't know if you calculated the weight of the water in all those buckets, but I thought I'd bring it up because the legs on your table look like they could use a cross brace. I can't see any - but you could simply put a piece of wood across the legs and screw that down.
Oh, and insulated any of the pipes you can (afford too). It does more than help your efficiency (energy used), it makes for more consistent temps. Lastly, white PVC is *not* light proof (even schedule 40 PVC). I just mention this because most people don't know this.
Just trying to be helpful.
Peace.
