If you have recently added algaecide, this can cause foaming for a short period. If this is the case, either wait and it will clear, or you could backwash some water out of the pool then top up with new water.
Sun tanning lotions, moisturisers and oils are the usual cause of this problem. Use Water Polisher to remove these impurities.
If this is not the case, check all pipework for air leaks.