Sponge ID good or bad
 

This guy been growing in my tank he's a slow grower wondering if anyone have any info dono were he came from but I think he looks good.

i have one of those growing in my tank too but i dont know what it is either

I'd consider it a good thing.

In general sponges are harmless, I took a zoology course this year and a big chunk of it focused on sponges. They truly don't do anything but sit there and filter feed. They are filter feeding machines! They can't even travel in your tank. The only concern would be how fast they grow and if they will invade your other corals nearby but by the sounds of it this guy is a very slow grower so nothing to worry about.
They're quite neat creatures one of the earliest simplest organless forms of ocean life. They are monoecious which means each sponge can fertilize itself aswell as other sponges around it (every sponge has male and female spores/flowers) and they are viviparous so there are live births no eggs or colonys like that. And even though the adult sponge is sessile (fixed in one spot cannot move) the larvae are free swimming and will move until they find a spot they like then they will settle down in that spot and never move again.

So your biggest concern is whether they will travel all over your tank or not but they are harmless. They're skeletons are made of calcium carbonate&silica collagen combination so they will use up some calcium in your water just like your other corals do when they grow :)

Hope this was helpful!