If you do decide to use any formalin (or combination) med, it's important to
- reduce temperature to 76 -78F (to increase/improve dissolved oxygen levels in the water)
- leave tank lights off 8-12 hours after dosing (re photosensitivity/reactivity of the formalin - & many other meds), fish are also generally more relaxed with subdued lighting
- at least 25% daily water changes (usually done just prior to dosing)
- have filter return gently splashing/rolling water surface to maximize oxygenation
- begin with 1/2 or even 1/4 dose, observe fish etc for negative reactions, then add remaining dose after ~1hour ... dim light if possible, but obviously sufficient lighting to observe fish respiration rates, significant lethargy etc: note it's common to see some mild stress reaction to meds, as long as fish are not gasping, spiralling, hovering at the surface or bottom etc
- have activated carbon etc on hand to help remove meds in case of negative reaction, also perform 25% - 50% water change
Many meds can interfere with N-cycle bacteria (another reason that 25% daily water change is recommended) so continue to monitor closely for the week following any treatments.
Shrimp can be sensitive to medications if they've just molted, so limiting food during any treatment is suggested, also don't begin a treatment if you see fresh casings.
If you decide not to medicate, daily water changes are always a great idea - if you're able to closely match tank & tap water parameters, 50% water change can help a lot.