Sand Question

[linz8392]

In January 2004 i started in the hobby with a 20 gallon. Then a few years later upgraded to a 46 gallon, then eventually to a 75 gallon reef tank.

I have continued to use the original sand and transferred it to each tank as i went, always adding more.

My DSB is currently around 3.5 - 4" deep.

My sand looks dirty all the way through, judging from what i can see through the front glass. I dont have a conch, or nassarius snails, but plan on getting some.

My question is this....do i take 95% of the sand out and add all new sand? Or do i just by the sand cleaning crew and let them do their work?

I think the sand is no longer filtering but instead releasing toxins into the water column.

SO....to replace pretty much all the sand, take the top inch off, and replace the rest with new sand, or replace NO sand, and just buy the critters and let nature take its course or replace some sand and buy the critters?

thanks in advance