I would say the green algae on the conk shell is normal, It appears that it is also a type of corraline algae. Some grow better with certain type of lights and also due to the water perameters, Ca and Alk. More live rock would be good but don't add it all at once as it can spike your ammonia in the tank. It would take quite a while for the base rock to be covered with purple coraline algae with what you have there. A skimmer should help with the brown algae as will regular small water changes until you get the skimmer and more live rock. I wouldn't add more fish till you get the skimmer. Good luck with the tank. Also siphon the crushed coral as melev said. I have a 40 G with crushed coral and I pull the nastiest looking stuff out of it.