Any medication marketed for ich will kill the biofilter regardless of where you are in the cycle. Your options are as follows:
1) Get a heater with an adjustable thermostat. Raise temperature to 86-87F. Recommended not to exceed 2 degrees change per 12 hours (some fish can tolerate more, depending what you have, but generally even if the fish tolerate high temperatures they do not tolerate rapid changes well). Maintain elevated temperature 2 weeks after disappearance of last white spots, then lower slowly to normal.
Advantage: biofilter survives this treatment, and the treatment will not be adversely affected by neglect. Disadvantage: if the fish are in bad shape, elevated temperatures below 86F accelerate the progression of the disease and you may have some losses.
2) Add salt at a rate of 1 teaspoon per gallon. Apply this dose three times at 12 hours intervals, then wait 3-5 days (based on 80F water temp) before beginning to remove it with partial water changes.
Advantage: it's fast and cheap, and effective. Effectiveness rises with water temperature (speeds up the parasite's life cycle, which makes it more vulnerable). Biofilter survives this treatment. Disadvantage: plants and some scaleless fish like loaches and catfish are not very tolerant of salt. Plants can be removed to a bucket for quarantine if desired and scaleless fish could be removed to the 10 gallon tank.
3) Medicate with any number of products marketed for ich.
Advantage: easy to follow instructions and quick to apply. Disadvantage: all medications for ich WILL kill your filter and restart the cycle. These chemicals are stressful to your fish, being based on either copper ion or low-dose formaldehyde, and they are even more stressful to invertebrates, so don't do this if you have snails or shrimp. Copper (malachite green) formulations are known to adsorb onto the substrate and remain toxic for long periods after removal from the water. Scaleless fish may also be intolerant of medications.
Pick one, if you're not comfortable with my advice alone then Google it a bit, but start one of these treatments within an hour of reading this post.