GH is extremely important; there would be far fewer fish dying in this hobby if aquarists understood and matched GH. I'll explain.
GH is the measurement of dissolved calcium and magnesium in water. Water is the most powerful solvent on this planet, which means it easily and readily assimilates what it comes into contact with when this can be assimilated. Each species of freshwater fish has evolved to function in a very specific water environment. In very general terms, hard water fish must have these minerals in the water because their physiology cannot function without them. While soft water fish do not need these minerals. Fish do not drink because they continually take in water via osmosis through every cell; this water, and substances dissolved in it, enters the bloodstream and internal organs. If the water is lacking these minerals, hard water fish cannot otherwise acquire them, that is how they are designed by evolution, and they weaken and slowly die. Death is often from other causes because the fish being so weakened cannot deal with them. In soft water fish this water passes through the kidneys which are designed to remove salts in the water. The result is calcium blockage of the kidneys, and the fish dies.
If the GH is 80 ppm, that is equivalent to 4 dGH, which is soft water, almost very soft. You are fine for soft water species, provided they are suitable for the tank size obviously. Your gourami are good. Your guppies are not. You could re-home them and select other soft water species (best for the guppies).
GH is the measurement of dissolved calcium and magnesium in water. Water is the most powerful solvent on this planet, which means it easily and readily assimilates what it comes into contact with when this can be assimilated. Each species of freshwater fish has evolved to function in a very specific water environment. In very general terms, hard water fish must have these minerals in the water because their physiology cannot function without them. While soft water fish do not need these minerals. Fish do not drink because they continually take in water via osmosis through every cell; this water, and substances dissolved in it, enters the bloodstream and internal organs. If the water is lacking these minerals, hard water fish cannot otherwise acquire them, that is how they are designed by evolution, and they weaken and slowly die. Death is often from other causes because the fish being so weakened cannot deal with them. In soft water fish this water passes through the kidneys which are designed to remove salts in the water. The result is calcium blockage of the kidneys, and the fish dies.
If the GH is 80 ppm, that is equivalent to 4 dGH, which is soft water, almost very soft. You are fine for soft water species, provided they are suitable for the tank size obviously. Your gourami are good. Your guppies are not. You could re-home them and select other soft water species (best for the guppies).