I noticed some spots on the glass of my Nauticam flat port. They look like thin mineral deposits and I can’t get them off. I always rinse the port with fresh water after dives, but usually don’t dry or wipe it afterward.

Any suggestions on how to clean them, or are they permanent?

Thank you,
Vitaly

I see the same on my housings. I was told it is the coating. I was also told to ignore it. YRMV.

Dry the port and water-contact optics after rinsing to avoid this, using a lint-free cloth. I try but it's not always top of mind after a dive. Can we really see water spots on a lens when shooting underwater?

Allowing water to evaporate on the glass is what causes this, the salts concentrate and it will eventually etch the glass, the same with anodizing on the housings. If you can't remove it with glass cleaner then it appears the glass has become etched. You can replace the port glass. The solution is prevention. I keep my housing covered after dives and it gets a long soak after each days diving before being dried off. I'm using a blower now from wolfbox, the high velocity blows the water off rather than letting it evaporate.

Hi,

I use Ceroxid (Cerium (IV) oxide).

It is a powder widely used as a high performance polishing agent in the glass industry. I bought some stuff on ebay but it shoud be available on internet shops as well. Watermarks are easily to remove and I was even able to remove small scratches with. I do it without polishing machine, so it takes a bit of time. But worth to do it.

Br Markus

2 hours ago, Muellema said:

I use Ceroxid (Cerium (IV) oxide).

I was told the glass has a coating, so any polishing compound might damage or remove it.

Hi,

any coatings on UW- ports are on the inner surface.

Br Markus

On 3/30/2026 at 4:55 PM, Muellema said:

I use Ceroxid (Cerium (IV) oxide).

I tried Ceroxid and it worked perfectly. Thanks a lot.

On 4/25/2026 at 9:24 AM, Vitaly said:

I tried Ceroxid and it worked perfectly. Thanks a lot.

How did it go with the coating?
I bought a Japanese cerium oxide paste ( Yanase YGC-C30 ) which is premixed and tried it on an AOI wetlens and the coating removal is really visible.
From what I understood Nauticam flat ports are also coated on the outside - did it remove the coating on yours?

11 hours ago, bghazzal said:

How did it go with the coating?
I bought a Japanese cerium oxide paste ( Yanase YGC-C30 ) which is premixed and tried it on an AOI wetlens and the coating removal is really visible.
From what I understood Nauticam flat ports are also coated on the outside - did it remove the coating on yours?

Which AOI wet lens did you try to polish? Is it possible that it’s an acrylic dome rather than glass?
I asked Nauticam support and they replied:
 "The outside of the port is uncoated glass, and there is an internal AR coating."

Edited 9 hours ago9 hr by Vitaly

5 hours ago, Vitaly said:

Which AOI wet lens did you try to polish? Is it possible that it’s an acrylic dome rather than glass?
I asked Nauticam support and they replied:
 "The outside of the port is uncoated glass, and there is an internal AR coating."

Great, thanks - I'll double-check with them for mine.
I tried polishing an AOI wet diopter (UCL 05-N) - it's coated glass. The coating is now off on the central part but I can't seem to remove on the edges - not sure how this affects images (the diopter was already pretty much unuseable, which is why i gave it a spin).