White film on glass after sandstorm & modding a powerhead

[Lemeshianos]

I have a powerhead that is set using suction cups. Every now and then it falls of and blows a sandstorm in the tank. For some mysterious reason, it only does that when I'm not at home. It's an evil powerhead I tell you!

Anyway it shifts the sand bed to one side of the tank and some ends up in my skimmer too. Did I mentioned that I used very fine playsand? Yeah, it's silica sand, I know the pros and cons, but it was just too good price compared to aragonite to turn down. On the good side, I don't have anything in my tank, as I'm waiting for a batch of live rock at the LFS. I only have base rock(DIY) that I tried to kickstart with a dead shrimp. On the bad side I was told that it will get very dirty after the cycle of the live rock that I will be getting. Well anyway it's there now, not much that I can do.

So after the first 3-4 sandstorms, when everything was calm, I noticed a white film on the glass. I used a magnetic scrapper and cleaned it. It need some scrubbing to go away. Not like the algae film that goes easily.
Since I noticed it after the first sandstorms, I assumed that it was some very fine dust from the playsand that was getting stuck for some reason on the glass during the sandstorm. It wasn't on the whole tank glass, but to the lower hal of the tank and some smaller patches on the upper half.
But thinking of it again, the base rock is DIY. I cured it in some small containers for about a month changing water daily, before it went in a fresh water tank for about 6 months. Before I used it in the saltwater tank, I let it dry and then gave it a good scrub. It's been in the tank for about a month and a half. I believe it leached out a bit of lime. My ph was in 9-9.5 for the first month and I was waiting for it to drop. It was during that time that I was getting this white film on the glass that I connected with the sandstorm.
Anyway after the 1st month, the ph was still high so I used carbonated water and it dropped down to 8.6-8.7. It's been there, stable, for the last two weeks and there is no white film anymore after a sandstorm.

Any idea what the white film was. Should I expect to see it again or not?

Also I'm thinking about modding the pump to add a magnet to it so I won't have to worry about losing suction and messing the sand. I've got some small magnets that seem quite strong but I'm not sure if I can just glue it on the pump. Should I glue and then seal it with silicon to avoid corrosion?