hey guys this december i went on vacation in mossel bay and i picked up alot of broken shells on the beach i just want to know can i add it to my salt water tank as a substrate becuase i have a hole bag full of them
I would not advise that because shells and big crushed coral can cause problems later on. Detritis (uneaten food and fish poo) gets trapped between the big particals and cause nitrate problems which in turn can be the cause of nuisance algae and cyano. Rather use fine substrate like aragonite or even better, use reggies play sand - very cheap, just wash it well until white before using it
Just remember if you want to replace existing substrate that is settled in already I would advise you to replace say a quarter of it and wait 1-2 weeks inbetween replacements to give the bacteria and pod population a chance to catch up and seed the new substrate.