changing out sandbed

[freddy]

So I started changing out my sandbed,i had a mixture of crushed coral and sand.I first started out with crushed coral,it started discoloring,then I had the bright idea to mix some old dead sand my buddy had into the crushed coral,I washed it good,but for the last 6 months,the crushed coral,always has alge growing on it.So yesterday I started changing it out,only about a quarter of it at a time,it wasn't that deep of a sandbed mabey an inch,I will do it slowly as to try and not cause a huge cycle,any ideas or comments would be appreciated.thanks.