Get rid of the algae. The risk of an algae overrun is too great. Anything in excess is horrible. I have gorgeous green/purple ricordias...ALL OVER my tank, I love and hate them, they make it hard to keep other corals. Algae, one established can become a huge nuisance very quickly.
Here's the thing, even if you liked it and it's pretty algae, do you want a reef tank with corals or with algae?
Ditto the planaria, get rid of them fast before they turn into a carpet. Do they harm anything? Well if they grow to huge proportions and then suddlenly die, you'll have big troubles.
V