My return is still spitting algae back into my pool when I vacuum. What am I doing wrong?

[CptAixel]

Last year all through the season I could only vacuum to discharge because any small living or dead algae would go right through the filter and come back to the pool. My local pool supply store said it's likely bad sand and should wait until I open next season and replace it. When I opened the pool, it was crystal clear with a layer of green algae all over the bottom. So here is everything I did when opening the pool:

I emptied the sand and inspected the lateral assembly. I ordered glass media. (Filter Glass - 40 lbs Bag - PoolSupplies.com) and refilled with 160lb
I shocked the pool with 2 gallons of liquid shock (

https://imgur.com/5XqED6W

)
I began vacuuming the next day and everything just spit right back into the pool.
I once again began vacuuming to waste and got 95% of algae off the bottom.
I refilled the lost water from the well.
Salt was super low (900-1100) so I added 200lb of salt.
It's clear I have a couple of problems, but the # 1 most concerning issue to me: How the heck do I stop the vacuum from returning the algae? I thought for sure the glass media would stop this issue, but it didn't even make a dent.
I'm going to lose my mind trying to vacuum this pool without losing water (and my chemicals/salt)

Any advice about the algae in the return would be immensely appreciated.

 

[Texas Splash]

The filter (and media) isn't your problem. In fact, you probably never needed to change the sand. You need to follow the SLAM Process to kill the algae once and for all. If you follow that page to the letter until you pass all 3 SLAM criteria, you'll see a difference. In hindsight, at opening you should've first vacuumed to waste any sediment at the bottom, rebalanced the chemicals, then gone right into the SLAM Process. Even if your water appears to be crystal clear with no signs of algae, at least do an Overnight Chlorine Loss Test. As it is right now your filter is overwhelmed and you need to maintain the proper SLAM FC level to get rid of it.