Inline chlorinator is causing my pump to lose prime

[BeckyT]

I have an inline chlorinator. It has a shut off valve. I only add tabs about once every 2-3 weeks. But when I do add tabs, my pump loses prime. You can hear the water chugging out as soon as I open the chlorinator lid. I had them put a shut off on it last summer and it seems worse than before.
Here are the steps I follow. I turn the pump off. Close off the chlorinator line which connects the chlorinator to the filter and then open the chlorinator. Any ideas on why I’m losing prime?

 

[mas985]

Air is getting into the plumbing. The chlorinator is a sealed system so opening it allows air into the plumbing which allows the water to flow out. The chlorinator should have two lines and you have to close off both lines to prevent this from happening.

 

[BeckyT]

Thank you. I wonder why the pool place that installed the shut off last summer didn’t tell me I would need two. Once liquid chlorine is easier to get, I won’t have to open it as much.