Help!! Newbie needs help from seniors!!

[azf]

Hi, I recently just set up my first marine tank, it's about 28x28x28cms.
Sand is I get from sentosa palawan beach, 2 nights ago, and a small black fish.

Live rock, button coral, sea fan, sea pen and mushroom coral from the marine shop at 32 plot pasir ris today.
I Put the live rocks and coral into the tank this evening, and now at night, maybe 6 hrs later, I saw alot of small sea fleas(not very sure what it is, can't manage to take a picture, very small) at the sand, and some on my corals. What are those? Are they harmful for my coral/fish? I intend to keep only 2 clown fish and 2 cleaner shrimps and some algae and sand cleaning snails.
How can I get rid of them if they are harmful?

[KaLiB]

Those small fleas are most probably copepods and/or amphipods from the liverocks. They are generally harmless and can be left alone. They are useful critters that help scavenge on uneaten food, detritous or even act as live food for some fish.

[azf]

Oh, so I can just leave them alone there? Thanks!!
And, do I have to add pro activated carbon? What does it do? It's advantage and disadvantages?

[azf]

And my mushroom coral is having white cloudy slime or something on some of the parts, is something wrong?

[KaLiB]

Activated carbon helps remove chemicals(like medications) & pollutants in the water. It also helps keep the water looking clean & clear. There are side effects to using carbon, it has been noted here to cause HLLE. You would also need to ensure your carbon is suitable for marine use as some activated carbon can only be used for freshwater setups.

Is this white cloudy slime coming from the center of the mushroom disc? If yes, it is due to stress. I would advise going easy on stocking up your tank, it might be stocked too fast resulting in ammonia/nitrite spikes that could have caused stress to your mushroom. Shifting it around can also cause stress.

Marine tanks are best stocked up slowly to allow the biological filter time to catch up with the new bioload. Ammonia & nitrites in marine tanks are more toxic than in freshwater due to the higher pH of the water.

On a side note, given the size of the tank, I would advise having no more than 2 fishes(that stay relatively small, 2-3" max) in there. 3 fishes is too many for a 28x28x28cm tank.

[azf]

Ohhh, I think I'll use only a wee bit of the carbon, haha. Ya, its from the center!! Alright, I'll wait for a few more days before stocking the fishes then, (: I'm releasing the one I caught at the beach, haha. So means I can't keep the snails and the shrimps too? Thanks so much for your replies and advice!! (:

[KaLiB]

Your welcome.

You can still keep the 2 shrimps but snails, you probably would only need 1 or 2 otherwise there might be too much competition for food and the snails would have insufficient food.

[azf]

I see, do you think those snails at sentosa Palawan beach can be used as sand cleaners? Haha. Cause I saw some that are rather colorful!
I hope my tank would turn out fine, thank you so much!

[azf]

and there seems to be a number of sea slugs in the tank, those with spikes on its body, is that alright?

[KaLiB]

I have not seen those snails from Palawan beach before so I cannot advise what are their care requirements & diet. Its best not to collect from the sea unless you know exactly what you are collecting. There's a danger of introducing unwanted critters into the tank and you may end up having to remove everything just to catch it back out. There's also the danger that you might pick up something venomous and get stung.

Sea slugs should be avoided as they have very specific diets. Each specie would only eat a specific type of food and nothing else. To make things more complicated, each specie consumes a different type of food. Most of them die of starvation as we are unable to provide a consistent supply of food. IMO, these are best left in the oceans as we are usually not able to provide enough food.