Tiny air bubbles through returns & waterfall

[elpietri]

Have had this inground, vinyl pool for 2 years now. Everything is working fine, nothing has changed, except...

1. I put too much algecide last fall and after I opened it this season it was foaming. Realized the problem, fixed it; fine.

2. However, I kept seeing the water cloudy and bubbly every time I turned the waterfall on (separate pump from the filter pump.) Drove me crazy thinking that it was still the algecide problem. Then I noticed that the filter pump was taking air after shutting down; not much, but enough for me to see it. I'm guessing the water level in the filter would drop by an inch or two overnight. Then, I also noticed that every time after I turn the system back on after opening the filter pump to clean the basket all the returns are throwing tiny air bubbles. It looks like a white powder coming out of the returns, and it actually turns the water cloudy a little bit, but a closer look reveals that they are tiny air bubbles. After the pump's been running for 3 or 4 minutes it stops doing it. However, the water fall keeps doing it forever. The water under the water fall turns cloudy, but they are actually tiny air bubbles as well.

I really don't want to think there is a vacuum leak, but after reading a few posts here I am afraid it is.

The questions are:
- How do I figure out what's causing it, where is it coming from?
- How to fix it?

Water itself is fine, chemical levels are fine. I have a pool heater and a booster pump for the Polaris.

Thanks a bunch,
Eduardo