Platy Has White Spot On Tail

[flip]

Tank size:20 gallons
pH:7.6 high range ph test says 7.8
ammonia:0
nitrite:0
nitrate:20ppm
kH:
gH:
tank temp:76F

Fish Symptoms (include full description including lesion, color, location, fish behavior):
she has a spot that looks like a grain of salt stuck to her by white cotton almost, the center is raised as if it is an actual grain of salt. her color is still good, she is hiding and is clamping her fins part of the time. she is preggers too.

Volume and Frequency of water changes:
25% once a week, top off in between

Chemical Additives or Media in your tank:
tetra aquasafe water conditioner

Tank inhabitants:
one male platy, he is staying next to her at all times, and some clamped fins, a platy fry that is a couple months old, two zebra danios acting fine.

Recent additions to your tank (living or decoration):
two silk plants a month ago, but nothing new.

Exposure to chemicals:
nope, just the water conditioner

Digital photo (include if possible):

 

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i almost forgot, i have 4 mystery snails in the tank too. also, last weekend our power went out for two days and the tank temp was down to below 60F. that wiped out a few of the fish in the tank.

 

[WILDER]

It dosn't look like whitespot, but hard to make out in the pic.
Any redness, or pinkness to the spot.

 

[flip]

no redness or any color, just white. could it be a fungus? it is the only spot on her too.

edit: she has started flicking against the plants, not all the time but she is doing it.

 

[WILDER]

For now I would add some pimafix. As it it turns out to be whitespot at least you can add a whitespot med to the tank with the pimafix.
If anymore spots appear the size of a grain of salt, treat for whitespot.

 

[flip]

ok, i will get some today and treat. thank you.

 

[WILDER]

Let me know how you get on if you don't mind.