The DPD dye is the same, but the powder has some advantages. The liquid DPD is subject to oxidation from oxygen and the reagents attempt to reduce this problem by having the pH of the dye solution be a bit lower and by adding EDTA to the solution and there are also phosphate buffers. There are side effects with the liquid DPD solutions that can occur depending on the pool water sample, such as having the sample be high in calcium which can precipitate as calcium phosphate. The powdered DPD is far less susceptible to oxidation from oxygen and requires less buffering and EDTA as a result.

So if you are in a pinch and don't have any powder available, you can use the DPD liquid instead. It's still more accurate to titrate with the FAS-DPD drops regardless of which form of DPD indicator dye you use.