Trash bag

[RichReef]

Without going into super details I want to create a temporary bladder to make a huge water change.

Would you trust a contractor trash bag?

It's a one time thing.

The only thing in the tank is a Yellow Tang.

 

[Isopod80]

The seams are nowhere near rated to hold the weight of water. If your planning to fill it even half way you'd likely have a mess. I would triple bag it at least and only fill less than half. Put the tang in a 5 gallon bucket with lid to be safe. Not only that but the bag could have chemicals/powders to prevent it from sticking similar to some disposable gloves. I wouldn't want that in my tank.

 

[RichReef]

I found some food grade ones for brining. That should work well.

 

[Isopod80]

The seams are still the main issue. I would definitely not have the fish in the bag for this. It's a risk I wouldn't be willing to take.

 

[Supa]

No way, maybe triple up or something. Water is heavy lol

 

[REEFTIDE]

Maybe purchase a tub at Walmart/ Home Depot and return it after? You won’t be out the money and you’ll have something more stable

 

[Just John]

Maybe purchase a tub at Walmart/ Home Depot and return it after? You won’t be out the money and you’ll have something more stable

I did this once to fill one with water for my kids. The sides bend out badly (on the cheap ones at least), 5 Gal buckets are cheap at the hardware store and can be returned. Imagine what a disaster it would be if that bag burst in your house. If you're married, you might not be for much longer

 

[Isopod80]

Besides, how are you planning for the giant bag of water to keep its shape? You mentioned making a bladder so I'm guessing no external support.

 

[Colt13]

I did this with a trash bag, used as a liner in a 30 gal brute trash bin. It worked

 

[RichReef]

Brute trash can with new water.
Overflow in trash can to sump.
Bag to drip old water into.
Force new water into sump.

The bag wouldn't be holding any weight.
Just a bladder.