There are a few techniques and tools that will help you catch fish without disturbing your aquarium.
Catching fish with two nets
The easiest approach is to use two fish nets, using one to herd fish into the other. Choose two nets based on the size of your fish and your tank. You could also use one small fish net to herd fish into a larger fish net. Keep in mind that nets with coarse netting move faster in water, but nets of fine mesh are less likely to snag fins.
Using food as bait
Have your net ready while you lure your fish to the surface with food. If you use flake food, wet the flakes and stick them against the glass in a corner near the surface. When your fish are busy eating, use your net to scoop them up from underneath. Do this a few times to get all of your fish.
Lowering the water level
Another method is to lower the water level in the tank to give your fish less room to escape the net. You may need to remove some plants and accessories in this case.
Using a fish trap
A fish trap, isolation tank or breeding unit is also a good tool for capturing fish without causing them stress.
Catching fish shouldn’t be stressful for you or your fish. Have patience as you try different techniques and find the one that works best for you.