This must be a large commercial pool. Knowing the size of the pool in gallons will be useful as a cross check, assuming some reasonable turnover rate for the initial design. The 30 HP is equivalent to 22,371 Watts of power [EDIT] actually higher because one must multiply HP by the service factor (SF) [END-EDIT]. Though itâ€™s hard to know the actual energy efficiency of the pump, itâ€™s unlikely to be much above 50% so that would mean around 11,000 Watts of output power which will be equal to 0.188165 * Head (in feet) * GPM. To know the relationship between Head and GPM, one would need to know the system curve and that can roughly be determined by knowing the diameter and length of pipe, though it gets pretty complicated depending on elbows and types of outlets. However, if you have a pressure gauge on the filter, then we can estimate the suction head to be some proportion of total head (usually 15% or so). Then you can calculate GPM from the formula. For example, if the pressure-side head is 200 feet (200/2.31 = 86.6 PSI) then 11000/0.188165/200/(1-0.15) = 344 GPM.
I think you can figure a worst case by allowing for something like 6 hours for one turnover and knowing the gallon size of the pool. If the pool is 100,000 then the flow rate might be 100000/6/60 = 278 GPM or thereabouts.
Also, take a look at this PDF file
for an actual commercial pool installation with a 215,000 gallon pool with a 15 HP pump that delivers 582 GPM at a Total Dynamic Head of 68 feet. One thing I forgot about in the above calculations is the service factor which for this pump is 1.15 (from the nameplate -- the text is wrong) so the actual power of the pump is 11185*1.15 = 12,863 Watts which is consistent with the 12.25 killowatt power consumption measurement (which is surprising since there should be some power losses from the motor itself -- brake HP which is HP times SF is supposed to measure delivered power from the motor without losses from impeller, not the energy input). The output power is 0.188165*582*68 = 7447 Watts so the efficiency is around 58%.
You should post at www(dot)troublefreepool(dot)com where a guy named Mark (mas985) can help you further since he knows fluid flow the best. There are also some other people with commercial pools who can help you.
(I've also E-mailed you this same info)