[Cougra]

I have to question whether there is even such a thing as old tank syndrome. I don't believe that it's possible for a properly cared for tank to crash without reason. I know that people talk about sand beds filling up with mulm over time or rocks becoming sink holes for detritus but I think that has to do with the "set it and forget it" mentality that people seem to have when setting up a saltwater tank.
People rely on the "clean up crew" to remove and process everything from the algae on the glass to the fish waste constantly being produced and the food that lands on the bottom of the tank. However the term "clean up crew" is extremely misleading since it's not really cleaning the tank so much as it's recycling the organics in the tank. Because of this people neglect the need for mechanical filtration, and regular removal of detritus by other means then solely relying on a protein skimmer and water changes.
There has been some improvement because people realise there there is some sort of fundamental flaw with the way substrates are treated and the current trend to move towards a BB tank allows people to see exactly how much detritus is produced in a tank and physically remove it. I believe the same results can be achieved in tanks with a substrate provided people understand that substrates do need to be cared for and not rely solely on the animals that burrow through it to keep it "clean".

I have had issues with my tank after it was running for 4 years, symptoms of what people would possibly consider old tank syndrome, ie hair algae, corals weren't opening properly, fish were lethargic etc. However, their was a root cause to all of this. It wasn't because I was using CC for my substrate, or that my rocks were too old, or that my animals suddenly became ill. These problems resulted from neglecting the tank due to bordom with the tank and other stressors in my life at the time.

I'll be willing to bet that if you asked anyone who had "old tank syndrome" about how their tank was set up and what their maintenance routine was you'll find that there tank wasn't properly cared for.