Do a good cleaning of your filter to get the flow back where it belongs and do a huge water change. Medications are almost never the answer. The problem is simple to state and to understand. If I add a biological agent to my tank that is designed to kill off fish bacteria, it will most likely kill all bacteria present. Unfortunately, some of the bacteria present are keeping my fish healthy, they are the beneficial bacteria in my filter. It is easier to get a good water change to remove most of the offensive chemicals from the tank and let the fish fight off infection than it is to deal with the chemical contaminants that come from killing off your biological filter.
All that we do in the hobby ends up being a balancing act. Fish tank water is not fit for human consumption but is the best we can provide for our fish. If I leave the chemicals in the water that make it safe for me to drink that water, it, the chlorine, will kill the fish. If I prevent any control of micro-organisms in the water, the fish will need to deal with them using their own natural resistances. If I can remove much of the contaminants with a water change and leave behind a healthy water system that gives my fish the best chance of survival. In most situations, now that I know better, I avoid using any medications and simply do my best to maintain a good water condition using water changes. My fish are seldom ever unhealthy and they recover quickly from many common problems. I do not believe that I am especially talented at fish medicines but my fish tend to thrive at all times.
In almost any case, your best bet for an ailing fish is a large, don't mess around with tiny 50% changes, water change. A fish that receives a 90%+ water change almost always looks better right away and seldom has much further in the way of troubles. This is a low tech approach but I find it especially useful for most situations. If a water change does not cause a rapid "cure", try a salt treatment. Salt causes most disease organisms to die at lower concentrations than ones that will harm the fish. That means that you can ignore almost any of the common medications if you dose your fish near their tolerance levels with salt and hold that concentration for a few days before reducing it with a water change. The end result will be fish stressed by the salt but alive, with the disease organism dead. As much as I admire the "miracle cures" of modern medicine, the simple salt treatment is still my treatment of choice in almost all cases.