Sometimes problems do arise, usually these are caused by something straightforward rather than an exotic and rare disease. If the reading is positive part water change, drastically cut back feeding and locate the cause. Never rinse any part of the filter in tap water as the chlorine will kill the 'friendly' bacteria. See instructions on box for easy method of removing sponge. A sponge may be rinsed several times before replacement.
New sponges are available.
Any excess food will pollute the water. During this period part water change more frequently and keep an eye on general fish health. Dealing with Algae -if the aquarium is on a window sill or in a sun room move it to somewhere out of direct sunlight. Products used must be fish friendly. As a nocturnal fish it will even do most of the work while you sleep.