Adding sand to established reef tank

[biggerstretch]

I would wash the sand thoroughly and add it slowly ... the sand will be dead and void of living bacteria however the dead stuff could cause an issue if you added it too fast... the solution to pollution is dilution. adding a 5 gallon pail of sand to a 2000 gallon tank is not an issue , adding it to a 75 gallon tank might be an issue ... just wash it outside , drain as much gunk out of it as you can and add it slowly .. dechlorinate the tank for what tap water may remain and possibly add some bacteria cultures like Dr. Tims just in case there is a spike from excess nitrates etc. If you just go slow you should be ok ...like all things with a reef tank slow is best ..