A, in the ecosystem, the energy flow is characterized by one-way flow and gradual decline, so to maintain the normal operation of the ecosystem, the device must be placed in a place suitable for lighting, and A is correct;

B, plant transpiration will lose a lot of water, so to maintain the normal operation of the ecosystem, the substance that must be supplemented regularly is water, and B is correct;

C, in this ecosystem, nitrifying bacteria (chemoautotrophs), lettuce and algae (photosynthetic autotrophs) all belong to producers, and C is correct;

D, the shorter the food chain, the more energy the highest trophic level gets, so the food chain where carp get the most energy is algae → carp, D error.

Therefore, choose: d.