I grow a ton of Calatheas and Marantas but mine have an advantage of being planted in the ground. They just do not make good long term houseplants. There are probably several factors affecting your plant, and when they affect it "all at once", it can lead to big problems. #1--most Calathea are not high light plants. This is a good rule of thumb to follow for light: if a plant has leaves that have red or maroon undersides, its a shade or low light plant. The red coloration is a genetic adaptation of rainforest plants that thrive in moderate to deep shade. The pigment is made up of specialized cells adapted to catching what is called "green light"...this is light that filters through the canopy layer, hits the ground and bounces back up. These plants with red undersides are specifically adapted to catching and utilizing green light. So putting your plant right in an unobstructed South facing window might have been a little too much light all at once. #2--almost all the Maranta and most of the Calathea have a sensitivity to not only chlorine but also mainly to fluoride in the water. Since most municipal water supplies are both chlorinated and have added fluoride for the kids teeth, you shouldn't use it for plants like these. Your water may also contain added ammonia, which forms what are called "chloramines" which are also bad for plants. All this will cause leaf troubles like the crispy edge. Using pure spring water, distilled or purified water is a good start. #3--Humidity is a key factor for these plants and misting and a pebble tray may still be inadequate, especially in a home in a Northern zone when it gets to be winter and you turn the heat on. Air conditioning is bad enough in summer, drying out the air but the heater is killer in winter. If you can stand it, you might have better results if you purchased a cheepo cool mist vaporizer from Walmart and ran it on a timer to cycle on and off in the close proximity of any plants you have that require higher humidity. You could group all your needy plants together maybe and hit them all at once. #4--5 fertilizer sticks is just way too much for a houseplant that is already stressed.And Calathea and Maranta can be resentful of too much fertilizer. Since you have trouble keeping your plant adequately watered in the first place, it would be much better to err on the side of underfertilizing and just use some 1/4 to 1/2 strength water soluble maybe once a month. #5--if you had white bugs AND webs, you probably had a mixed infestation of mealies and mites. The webs are from the mites, mealies don't build webs. But mealies do infest the soil and also lay eggs in the soil. Calathea and Maranta are rhizomatous plants, and mealies can attack the plant below the soil level. To be certain they are gone you may need to use a systemic pesticide that goes into the soil, like Bayer, on a regular basis. Your plant sounds like it is trying valiantly to make a comeback and you sound like you did your research pretty well. Just give it time.

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The first and absolutely necessary step is to get a comprehensive water test from an independent lab. Go to http://www.epa.gov/safewater/labs/index.html to locate a certified lab near you. This is a MUST DO because without it everything is a guess. A quickie water test from Sears or a water softener company won't be as accurate (and possibly not as competent) as from a certified independent lab. With those test results we can speak intelligently about what needs treatment and what you want treated.

Repotting is different than potting up. Your plant will benefit from a repot if the soil it's in is inappropriate/ performs poorly (usually due to excess water retention, but other considerations might also be factors) or if roots are congested to the point the root/ soil mass can be lifted from the pot as an intact unit. Where you live determines the repot timing most beneficial to the plant. Generally speaking, the month immediately prior to its most robust growth period is best. I would choose a very coarse soil that holds very little water (and lots of air) in the spaces between soil particles, even when the soil is at container capacity (maximum water holding capacity). This means the primary fraction of particles should be much coarser than peat or ground pine bark or composted forest products. Airy soils that drain extremely well and hold little or no excess (perched) water are easiest to grow in, and make it much easier to reliably bring along healthy and attractive plant material. Al