Got busy all summer and fall. Can't remember the last time I topped off the salt in the brine tank. Might have been August-ish. I realized it today and the tank was full of just water with some brown gunk in it. I vacuumed the water out (to keep it from overflowing) and filled it with salt. Started a regen cycle. Is there anything else I need to do or be aware of?

Nope, let it do its thing.

Doesn't hurt anything except having to suffer through hard water.

10-4. Thanks!

I would do a 2nd regen cycle to clean it further. Here are some tips (from my experience).

1) When salt bin drops to 50% fill it to only 75%. I found when I top it off 100%, a large air gap builds up underneath which gives the illusion there is still plenty of salt. But the air gap doesn't isn't supplying salt for proper regen cycles to clean the media filter.

2) Check the level monthly & use an ice pick to break up the air gap below the salt so everything goes down.

3) Program the softener settings to regen based on gallon usage, not timed schedule. This will conserve salt.

4) Buy this Wi-Fi based Pentair salt level sensor. It's not super accurate, but will give a "general sense" of the salt level from the smartphone app. It will also e-mail you when salt is very low.
https://www.lowes.com/pd/Pentair-Connected-Salt-Level-Sensor/5001446993

5) Since that Pentair salt sensor uses 3 AA batteries, I bought this to power it using the AC adapter so I never need to replace batteries. This particular one generates 1 amps needed to power the device correctly (the one's on Amazon didn't work).
https://www.batteryeliminatorkits.com/product-p/3aa-eliminator-kit.htm

Thanks. I've been good about keeping it topped off every couple of weeks for years and never the air gap issue. I know what you're talking about though. This summer and fall were just different. Wife was working crazy hours and I had both kids a lot. Also been booked with places to be or things to do every weekend for the last month and half or so. Got caught up with everything and just forgot to check it.

I'll definitely need to look into the salt level monitor. That sounds super helpful.