Eric . . . Not knowing the tractor you are looking I will state the most every loader manual I have ever looked at says that you need BOTH types of weight on your tractor to safely use the loader. My New Holland loader manual says FLUID FILL plus WHEEL WEIGHTS plus a
BALLAST BOX.
Now most of us don't do all that.
I would suggest fluid fill AND some implement or a ballast box. On my Kubota I use fluid filled rear tires AND a box blade.
The reason for all the rear weight is that many of the front end loaders are very powerful and to achieve proper balance so the machine can actually USE the capacity of the FEL you need to have a lot of weight on the rear of the machine. It is interesting that both light and heavy tractors still require a lot of weight on the rear of the tractor, that is largely due to the fact that much of the tractors weight is fairly far forward (the engine is typically in front of the FEL attachment point) on a small tractor. So to achieve balance on any tractor, you need ballast, and if you read the owners manual, you need a lot of it. Again, most of us don't have all the ballast that the manual says we should have (I don't on one tractor and do on the other) and what that means is that most of us actually can't use our FEL to its maximum capacity under the most adverse conditions . . . but we can use most of it most of the time and that is usually good enough.
BTW, I'm not sure what "Mg" is in the tire, there are several types of fluid typically put in tires, basically they are mostly water mixed with something. Calcium is common. "Beet Juice" is common. Wiper Fluid is fairly common. Anti-Freeze is unfortunately still being used . . . it is very poisonous and if the tire leaks can be a major hazard and easily will kill a pet or child who tastes it (about 1 tablespoon of anti-freeze will kill a very large dog) and even more unfortunately, it smells sweet and attracts animals to it.
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