I use dilute hydrochloric acid to keep my galinstan looking like mercury. The oxide doesn't just increase wetting it its the sole cause of it. You need at least 0.1 M HCl to get maximum surface tension and to keep the surface shiny. Paper on it
0.1 M is about 0.37% concentration. Any concentration of HCl under 5% is "safe" to handle and only over 15% is considered to have the ability to case serious harm. Muriatic acid from a store is usually around 28% - 36% but they don't always give an exact concentration. You'll either have to buy some from a chemical shop that specifies or do a titration on the common stuff.
I just started some trials with 12 sealed tubes of about 1 ml galinstan each ranging from pure water to 1.0 M HCl. Cool stuff. (Sorry for bad quality, phone camera glass is shattered) Only been a few hours and I plan to leave them for months but as of now at 0.1 M and higher concentrations it looks perfect. 0.05 M looks decent, lower and its no longer shiny. The highest (0.5 M - 1.0 M) have visible hydrogen forming from excess acid attacking the metal itself. So far seems like 0.1 M to 0.2 M HCl is best. Water only vs 0.2 M HCl bath
And try to only get clean metal in the acid without tons of oxidation or the dilute acid wont be able to dissolve it all. I always keep my galinstan under water and my syringes full of water when I work with it as soon as its cooled from the alloying heat to slow the oxidation.
In case you don't know the process going on here, the acid can react with the gallium oxide as it forms from the dissolved oxygen in the water. The products of this are gallium chloride and water. Gallium chloride is very soluble in water so the small amounts are invisible. The dilute acid also slowly (very, very slowly) reacts with the gallium, indium, and tin to form the metal chlorides and hydrogen gas. With dilute levels like 0.1 M the metal being lost is negligible. The container is completely full with water so no new oxygen can be dissolved like it would if there was air present above the water.
I'm thinking that if it is in a sealed container the oxygen dissolved in the water will eventually be consumed and converted to H2O and the system will reach an equilibrium. But I'm no expert. If it can last a year or more I'd be satisfied. (Making non toxic liquid metal snow globes with the centerpiece floating on galinstan.)
Liquid metal is fun to work with. I especially like watching it bounce and rebound off the glass when its in a small enough amount to form a bead. I will update this with my results in weeks or months. Best of luck!