I just realized that I added about 4 cups of water to 4 cups of flour for my ciabatta dough. It only calls for 2 cups, but I added 4 for some reason. It’s been rising for a bit over 4 hours and there are a lot of bubbles, which I’m happy about, but it’s very runny. It was a bit sticky when I mixed it but it can pour like a thick soup. How do I fix it? Will it ruin the air bubbles if I add more flour?
Perhaps some baker's math is in order to understand what's happening here and what direction your fix should be aiming at:
4c flour -> 500g 2c water -> 480g
This means your recipe has a hydration1 of 96%, which is really high, even for ciabatta. It's doable, though, as for example this post cofirms. (Typical values for ciabatta are somewhere in the 75% range.)
Your current dough has:
4c flour -> 500g 4c water -> 960g
Resulting in a hydration of 192%. Or, as you noticed, yeasty soup.
Having checked this math, you have to get the flour level up to at least the original value, that means somehow incorporating another two cups of flour. But then your other ingredients will be off, too, especially salt, so add again the amount of the original recipe, basically doubling it (as demanded by the flour as base for the calculation). Same goes for all other ingredients except yeast.
Yeast on the other hand is a totally different subject. In the last four hours, the yeast has been active and growing. Adding again the original amount would likely be an overkill. Depending on your general bread baking philosophy and recipe, add either a fraction of the original amount or simply wait until the existing yeast has done it's job. (That's what I'd do...)
With the relatively large amount of flour plus the salt I'm not sure whether incorporating it during the stretch and fold would be possible. (For smaller amounts, heed ElendilTheTall's advice). I'd consider sacrifying some bubbles and stir or mix gently.
1 also called Baker's percentage, i.e. the ratio of water or other ingredients in relation to flour weight.