Do gunge / slime mixes weigh the same as each other / water?

If I had a dozen balloons, 9 filled with water and 3 with gunge / slime, of the same volume (1L) would the gunge filled ones sag down further?

Just thinking if I had them hanging from a pole or something and told a willing victim to stand under one while I pop it if they'd be able to easily identify between water and goo?

Without looking anything up, I can definitely tell you that gunge is going to have a different density to water. The inclusion of gunge powder forces a re-organisation in the average arrangement of the molecules; ergo the density will be different. At a guess I'd say that generally gunge will have a higher density than water, though it doesn't really matter if it's a higher or lower density to you, only that it's different enough to be noticeable.

Also, the other factor you may not have considered is that gunge is generally much more opaque than water - so the balloons will appear different in colour as well as in weight.