[sirreal63]

Cooking is not needed but it can help greatly. Acid is the trick to getting the rock clean. It still has biological matter on and in it. Sponges, algae, etc. which are dead. I cleaned mine by soaking in a 50/50 vinegar solution for a couple days, removed all the dead and decaying matter you can see first then scrubbed very well with a brush, rinsed them and let them dry. Adding them to the tank caused no issues.

Phosphates can be bound in the outer layers of rock and the acid will dissolve most of this as well as eat up the biological matter. Cooking the rock serves the same purpose...the bacteria eat the available nutrients until they are gone. Acid just does the initial cleaning in days instead of months. I am not worried about nutrients inside the rocks as it is food for the future bacteria populations. Getting the rocks clean and as much of the outer layers off is what is important.