You need to post all your test results here before anyone can help you.

Your problem is probably from a low level of residual free chlorine - then the algae started to take over. Again post your levels (including CYA) and we can tell you what level you need to get your free chlorine.

Chlorine starts as FC (free chlorine) - if it changes to CC (combined chlorine) then it means it is fighting some organic material in your pool. TC (Total Chlorine)=FC + CC

Get a good drops based test - there should be a 6-way test available at Wal-Mart to use immediately, however you will really want to spend the money and get a good one. There is one available on the sister site http://www.poolsolutions.com, or Taylor makes a good one that will work