Corner silicone has.... mould? Algae?

HI all, I recently bought a used 50 gallon tank, and gave it a good clean on the weekend. My only concern is the silicone seals in the corners (all 4 sides). They've got little blackish specks all thru the silicone. Strangely, the seals around the bottom of the tank do not have this, only the seals going up the sides. I scrubbed the tank and the silicone really well with a coarse scrubber, initially using a water/vinegar solution, then with a water/bleach solution. The bits in the silicone didn't budge.
I scraped some similar bits off the back glass with a razor blade, it came up very clean.
Should I be concerned about this silicone? I didn't want to have to reseal the tank! I'm thinking this is just algae that has settled into the silicone over time... and figure if it's not coming off when I scrub the heck out of it with a bleach solution, it's not going to affect anything in the tank. I'm thinking it's really just a 'cosmetic' issue at this point.
Thoughts/advice?
Thanks very much.

 

It’s definitely a mold under the silicone. I’ve had tanks like that before. As long as there is no leaks I haven’t had any issues with the discoloration. Just isn’t nice to look at. It’s imbedded into the silicone so it shouldn’t cause problems with fishes health. However for future assurance to not have a leak pop up I would just go ahead and reseal the tank now while it’s empty and save yourself some trouble later.

 

The tank has no leaks... are you saying that the growth of the mould could potentially cause a leak down the line?

 

The tank has no leaks... are you saying that the growth of the mould could potentially cause a leak down the line?

Yes, it could very well be a possibility. Although I have never had a problem with it personally I would recommend resealing the tank just to ensure no future leaks happen. It’s like rust on a car. It’s okay for a little while until it spreads and becomes a problem.

 

Ok, good point. Sounds like I have a new project on my to-do list Thanks!

 

Don't be tempted to use silicone with anti-mould ingredients in it though, the fish may not like it. I used Dow 781 Acetoxy silicone to seal my tank and I've had no issues.

 

No worries, I'm probably going to get the Aqueon one that my LFS carries.

 

No worries, I'm probably going to get the Aqueon one that my LFS carries.

Hopefully that stuff is cheaper where you live than where I live. I've just done a search for it and it's nearly £18 for a tube. I only paid about £5 for Dow 781.

 

I haven't checked around yet, but the price I'm seeing at my LFS online store is about the same price as yours in the UK (just under $30 Canadian Dollars). Same on Amazon.ca. Will do a little more digging