Best sealant for pool grout? Pictures of my tile

Hey guys! I have a small pool leak somewhere near the top tile portion of my pool I have not found yet. Good news is the waterline settles down an inch above the skimmer, but I'd still like to seal the grout. What sealer should I use? And is it a good idea to apply silicone over this grout? There are a lot of places where the grout is worn giving a good gap to fill with sealant, but I'm concerned doing it all over will make it hard to clean, or may mildew. We scrub the tiles almost weekly.

I'll probably use the same sealant for the concrete gap, although that seems more aesthetic right now.

I've found so far:
Vulkem 116
White 3M Marine 5200 Adhesive

Thanks!

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