Gluing hardscape above waterline in an already-stocked tank

[WhistlingBadger]

I finally got my waterfall hooked up, and woo is it fun. But now that I see how it's going to flow, I need to make a few modifications, gluing a few fake rocks into what will be the water flow to direct it where I want it to go. This is complicated by the close proximity of live fish, and I'm trying to decide how best to glue the needed pieces in place. If you're into this sort of thing, read the info below and tell me what you thin.

Some info:
I have the waterfall pump turned off, so however I glue this, it won't be flowing into the tank or directly in contact with the fish or their water until after it cures. But it will be in the tank, several inches above the water line. The part I'm gluing is on a wide shelf, so there is no possible way the glue itself could come into contact with the water. It will be a small amount of glue: Two beads about 3-4" long.

Aquarium silicone would be ideal for the application because it would make good seals, but I'm a bit worried about the acetic acid vapors while it cures. I believe I could put a fan on it until it's cured; the amount of acetic acid that actually found its way into the water would be minuscule. But I'm still uneasy about it because I've never used the stuff in the near vicinity of live fish. Logic tells me it would be fine, but my gut is uneasy.

Epoxy is probably a no-go, since a little reading indicates it seems to give off all sort of weird gasses.

Gel cyanoacrylate (superglue) might be my best bet. I have often used it to good effect. But it isn't ideal for the application as it is strictly adhesive; it isn't worth crud for filling gaps and sealing.

Not sure how much sense this makes or how to better describe it. @Wills @GaryE and @Boundava , you've messed around with this sort of stuff some; any ideas?

 

[Colin_T]

superglue or silicon

 

[FranciscoB]

+1 superglue or silicone.
The silicone can be solvent-based (acetone), or hot-melt. The latter has advantages such as curing very quickly and having no fumes. Glass surface must be impeccably clean and dry for it to adhere, and it does not adhere as strongly, so useful for some applications but not others. For sealing void spaces, it might work well. Otherwise regular silicone while maintaining water level somewhat down and waiting for it to cure.

 

[WhistlingBadger]

I went ahead and went with the silicone. Already second-guessing that decision, but Iacta alea es, as they say.

 

[Magnum Man]

If your tank is covered, open it while the silicone is curing… if it’s uncovered you’ll be fine

 

[davros]

IIRC you can get CA that has body or you can add it yourself - glass beads

 

[Boundava]

I finally got my waterfall hooked up, and woo is it fun. But now that I see how it's going to flow, I need to make a few modifications, gluing a few fake rocks into what will be the water flow to direct it where I want it to go. This is complicated by the close proximity of live fish, and I'm trying to decide how best to glue the needed pieces in place. If you're into this sort of thing, read the info below and tell me what you thin.

Some info:
I have the waterfall pump turned off, so however I glue this, it won't be flowing into the tank or directly in contact with the fish or their water until after it cures. But it will be in the tank, several inches above the water line. The part I'm gluing is on a wide shelf, so there is no possible way the glue itself could come into contact with the water. It will be a small amount of glue: Two beads about 3-4" long.

Aquarium silicone would be ideal for the application because it would make good seals, but I'm a bit worried about the acetic acid vapors while it cures. I believe I could put a fan on it until it's cured; the amount of acetic acid that actually found its way into the water would be minuscule. But I'm still uneasy about it because I've never used the stuff in the near vicinity of live fish. Logic tells me it would be fine, but my gut is uneasy.

Epoxy is probably a no-go, since a little reading indicates it seems to give off all sort of weird gasses.

Gel cyanoacrylate (superglue) might be my best bet. I have often used it to good effect. But it isn't ideal for the application as it is strictly adhesive; it isn't worth crud for filling gaps and sealing.

Not sure how much sense this makes or how to better describe it. @Wills @GaryE and @Boundava , you've messed around with this sort of stuff some; any ideas?

I'm sorry what size tank is it? And how high are the areas that you need to fill in comparison to the height of the tank? I'm only asking because one option would be to lower the water level for a week till allow the silicone to dry out of water. I would not recommend letting silicone set underwater with fish. The acetic acid is not going to be good for the tank.
Super glue is an option however in my experiences with super glue it crystallizes so fast underwater that it is almost ineffective in long-term adhesion. You can also do what I suggested above lowering the water level in the tank temporarily and use the super glue out of the water to glue it on, let it set, and then refill.

Depending on the gap size you could also use the pond expanding foam. That is safe for aquatic creatures almost immediately after it's set. I haven't used it in a while so I'm not sure what the cure time for that is. If you do use it I would apply it like I recommended above by lowering your water level temporarily and letting it set and then just refilling the tank.

Sorry if my response is a little late. I've been battling cats in the house so haven't been to the forum in a while.

 

[Boundava]

Never mind this is your 55 gallon right, sorry I'm enjoying some coffee before work and I'm not awake yet.

 

[WhistlingBadger]

I'm sorry what size tank is it? And how high are the areas that you need to fill in comparison to the height of the tank? I'm only asking because one option would be to lower the water level for a week till allow the silicone to dry out of water. I would not recommend letting silicone set underwater with fish. The acetic acid is not going to be good for the tank.
Super glue is an option however in my experiences with super glue it crystallizes so fast underwater that it is almost ineffective in long-term adhesion. You can also do what I suggested above lowering the water level in the tank temporarily and use the super glue out of the water to glue it on, let it set, and then refill.

Depending on the gap size you could also use the pond expanding foam. That is safe for aquatic creatures almost immediately after it's set. I haven't used it in a while so I'm not sure what the cure time for that is. If you do use it I would apply it like I recommended above by lowering your water level temporarily and letting it set and then just refilling the tank.

Sorry if my response is a little late. I've been battling cats in the house so haven't been to the forum in a while.

Yeah, it's in the 55 paludarium. Already got it done with silicone. I just left the lids off for ventilation, and left the waterfall pump off until I couldn't smell vinegar anymore. Worked great!

 

[Boundava]

Thought I was going to be late in reply, never got any notice of you mentioning me. Glad you got it done though.