Can I partially reseal a tank?

[pseudorand]

I just bought a used 120gal made in 2003. It doesn't leak, but the thin black silicone along the vertical edges is in horrible shape. I can peel it off with my bare hands in some places. The bottom of the tank, however, has a much thicker bead of clear silicone that appears to be in mint condition. It's looks so pristine and is so perfectly laid that I think it may actually be a gasket of some sort rather than silicone. It does appear to have more of the black silicon in the seams underneath.

Because the silicone on the sides is in such bad shape, I think I should re-seal the tank before stocking it. However, I'm reluctant to touch the clear silicon or gasket or whatever it is on the bottom because it looks fine.

Does anyone know if I can scrape off and replace just the silicone joining the four vertical pieces of glass? Or will the tank likely leak at the four bottom corners because my new silicone and the old silicon under the gasket aren't bonded?

 

[xxkenny90xx]

I would recommend redoing all of it or none of it since like you said the old and new silicone won't bond together. Even if you do all of it (which I have done successfully) it isn't great since you aren't replacing the silicone in between the glass in the corners. Maybe adding another layer of silicone over the existing on the sides might add a bit of protection?

 

[Dragon52]

Redo the whole thing is the best course of action.
But if the bottom seams look really good I might try what you want to do but I would fill it full of water outside afterwords for a week to make sure it doesn't leak.

 

[pseudorand]

I guess my real question is what the clear thing is at the bottom. Is it just silicone or do large tanks use something different (i.e. a gastket or something) that I can't easily reinstall. Has anyone either built or re-sealed a large tank before?

 

[ca1ore]

Can you show a couple of pictures? Doubt it is a gasket, though I suppose anything is possible. Resealing is primarily about aesthetics and protecting the structural seal. If there is something amiss with the latter, no amount of 'resealing' is going to help.

 

[Bigwrasse]

definitely redo the whole thing. I tried this recently with same size tank and after a month the tank blew out all over my floor

 

[pseudorand]

I ended up redoing the whole thing. I'm pretty sure it wasn't a gasket because it came off just like silicone. Some previous owner just resealed only the bottom of the tank with clear silicone. (S)he did a very "professional" job in that it looked very smooth. Who knows if it did anything to keep the water in though. Perhaps it protected the original, ageing seal.

In any case, I scraped the whole tank clean and re-sealed it. I'm filling it for the first time now. I'll let you know if it leaks in a week or so (or perhaps sooner if I did a bad job).

Resealing lesson learned: I ended up resealing it twice because the first time I used the largest "cut corner" of my smoothing tool (16 something, mm maybe). I didn't put enough silicone down for a corner that wide, so I ended up with air bubbles. I decided to just redo it again rather than find out the air bubbles caused a leak a year from now once it's stocked.

 

[pseudorand]

definitely redo the whole thing. I tried this recently with same size tank and after a month the tank blew out all over my floor

You tried resealing just part of the tank? Or did you re-seal the whole thing and it still blew out? Now I'm worried I have to wait a few months to stock it to make sure my new seal is good. I guess I'll probably have to wait that long anyway to cycle the thing, but still...