Reddit mentions of GoPro Anti-Fog Inserts (GoPro OFFICIAL ACCESSORY)

I took my Gopro to Thailand in February. I shot mostly at 1080p @30fps. This frame rate will let a good amount of light in. Choose a higher frame rate if you plan on filming fast moving objects and want to use slow motion. Increasing frame rate can reduce light input, though. My still shots all came out a little blurry, but the video was great. I used a retractable pole that I could sneak under rocks and around crevices where a lot of the fish and other creatures hide.

For color correction, I brought some cheap thin filters that go inside the camera housing, over the lens . They were a pain in the ass to line up and keep clean. I would recommend one of the external filters you linked. The deeper you go the more colors you lose. Starting with red and going around the color wheel, that is why they have different shades. I never dove down below 18m and used the red filter. I also adjusted colors and contrast on the computer using GoPro's Cineform software.

A MUST when you are diving (especially in a humid environment) is to bring a Fog Insert to absorb moisture. The tiniest bit if moisture in the housing will fog up the housing once you are at depth and under pressure. Here is GoPro's version, but there are cheaper options:
http://www.amazon.com/GoPro-AHDAF-301-Anti-Fog-Inserts/dp/B009QXFFYS

The gopro used to ship with little anti moisture packets that you would put in the case to prevent the lens from fogging up. If you are having that problem, it might be worth looking into.

Edit: http://www.amazon.com/gp/aw/d/B009QXFFYS?pc_redir=1409968434&robot_redir=1

They are these ones:
http://www.amazon.com/GoPro-AHDAF-301-Anti-Fog-Inserts/dp/B009QXFFYS/ref=sr_1_1?ie=UTF8&qid=1450760280&sr=8-1&keywords=gopro+humidity+strips
The GoPro brand. I have not bought them yet because of the blue circle spot and not the light red/orange.

Depending what go pro you have, antifog these are good to have in the case so it doesn’t fog up:)

Totally disregard if it’s one of the new ones

five bucks cheaper on amazon.

We found out (the hard way) that the plastic cases do fog up pretty easily - such as our launch here https://www.youtube.com/watch?v=9-R5FJCwQOE

It turns out that the GoPro cameras dissipate a lot of heat, so you actually don't even need to typically put them in the case unless you are really concerned of a water landing, and they should be OK for the duration of most typical HAB launches.

All of our past few launches have just been the exposed GoPro and they have all been fine, without any fogging/condensation - https://www.youtube.com/watch?v=-qNUDRwAlL0

If you must use the plastic case, you can get some dessicant packs (anti-fog inserts) such as these: https://www.amazon.com/GoPro-AHDAF-301-Anti-Fog-Inserts/dp/B009QXFFYS/ref=sr_1_3?ie=UTF8&qid=1473102600&sr=8-3&keywords=gopro+dessicant

We haven't used them ourselves, but they should do the trick.