Salt Creep or Tank Construction?

[TheAgileSlug]

I'm refurbishing a Reef Savvy 40 gallon cube tank and when looking at the overflow, I noticed the below rings around the bulkhead holes. I did my first fresh water test and it held water for over three days. This tank has a layer of glass and a built in 'base', so I'm hoping it's just the way the base was sealed to the bottom...

Can anyone tell me if this is a result of old salt creep, or perhaps how these thanks are constructed?

Disclaimer: Please set aside comments on all of the clear silicone within the overflow, the previous owner apparently let a tube loose in there and I'm in the middle of cleaning it up. I might end up taking the overflow off and resealing it.

 

[Jason_MrFrags]

if previous owner used that much to seal up a leak your best to remove it and reseal. Although without practice it may end up looking the same. The rings should be from the bulkhead seals but looks like those might of been silicon-ed in place probably from previous owner as well.

 

[TheAgileSlug]

if previous owner used that much to seal up a leak your best to remove it and reseal. Although without practice it may end up looking the same. The rings should be from the bulkhead seals but looks like those might of been silicon-ed in place probably from previous owner as well.

I'm just not sure if they used it to seal a leak on the bulkheads or the tank. After I cleaned up a lot of the silicone around (and actually IN) the bulkhead holes, it held water without any leaks.

My bigger concern was that it might be salt creep on the bottom, which I do not want to try to remove. I should probably take the time to remove and re-caulk the overflow though.