adding crushed shell

[oscarxj]

I have an established 75 gallon fish only aquarium with 40 lbs live rock and I am looking at adding 10-15 more lbs of crushed shell.

1. Can I do this?
2. If I can what is the best way to do this.
3. What is a good time to do this? Water change or whenever?

[jonthefb]

1. Yes
2. Make sure the crushed coral is rinsed off well before hand or else your tank will be very cloudy. Take it a cup at a time and pour it slowly over the top of your existing substrate. Keep doing this until you have added as much as you would like.
3. Absolutely DO NOT do this during or after a water change. If you have crushed coral in the tank and are vacuuming it out for a water change, you are going to be removing a significant amount of the bacteria and critters that are beneficial to the system. If you were to add new crushed coral on top of the stress of the water change, it could be enough to severely shock your systems and cause major problems. Try and add the new crushed coral several weeks before your next scheduled water change!
Cheers~!
Jon