Is there a serum phosphorus level you would consider too low to safely perform hemodialysis?  

I actually do. I have previously published reports of 2 patients who developed recurrent encephalopathy due to dialysis-induced hypophosphatemia. They were treated with adding phosphorus to the dialysis fluid and the episodes did not recur (Koganti & Sam, PMID 31940631). I definitely do not want...

Phosphate (P) removal on hemodialysis (HD) is dependent plasma P levels, the volume of blood passed through the dialyzer and the type vascular access used. As HD removed by diffusion, as P is removed during HD the concentration gradient falls lessening the removal of P during the dialysis treatment...

There is no safe level as hd mainly removes intracellular phosphorus and low phosphorous level likely due to poor nutritional intake, assuming no binders.

Clearly would want phos greater than 2 and more likely 2.5. If phos runs in the low 2, I would likely add phos supplements if diet does not increase it.

2?