I can't find a couple of my saltwater fish in my 75 gallon tank. There are so many nooks and crannies for them to hide in the live rocks. I suspect they died. I wish to locate them, so their dead bodies won't be decomposing and releasing toxins. Any suggestions as to how to locate them?
Sometimes as they start to decay or as other fish nibble at them, parts of them become small enough to get sucked into filtration. Check filter by partially disassembling it and remove any questionable chunks. Also, check filter intake to see if anything is stuck to the underside, or less visible side of the intake.
Look in any caves, nooks and crannies of decor or plants for where bottom feeders may have dug them under in hiding for later feedings.
Do a water change with a gravel vacuum. Moving the gravel vacuum along all bottom parts of aquarium is something that should routinely be done anyways, but this would be a good time to start, OR to do an extra one, and may help you spot something that's blending in well. Fish tend to lose their vibrant colors after they have passed away.
Consider you may not find them, and don't be too worried, sometimes other fish help eliminate this as an issue by eating "floaters".
Test your water a day after the 10-15% water change to look for spikes in ammonia, and continue every couple days until levels are within safe range. If levels are fine, no worries - just keep an eye out for "fuzzies" where the decaying matter has blended and is now growing a fungus. This fungus is NOT safe and should be removed.
Good luck. Dead fish mysteries are common in the fish world.