Air in my system

[RENOPOOL]

After having my pool for three weeks now with no problems. Out of the blue today my pressure went down and I could see lots of bubbles inside the glass on my pump filter basket. I turned off the pump and open the air vent on top of my filter to let out the air out. Turn on the pump and everything was back to normal. What caused the air to get in my system? The only thing I noticed is that we had a lot of rain today and my pool was almost to the top of my skimmer (I keep it about half way up). Could the hard rain some how caused air to get in? It had stopped raining for about 2 hours be for this happen. I would think if I had a major problem once I let the air out and turn it back on I would still have a problem. The pump has now been running for over three hours since this happen and still everything is normal. I am new with this in ground pool stuff and was wondering if I had some kind of problem.
Please help!
Thank you!