gray growth(?) on guppy fins

[nisi]

Help appreciated asap as this seems to be progressing very quickly. TIA

1~What type of fish is afflicted? In addition, please describe what is wrong with the fish to the best of your ability (i.e. cotton like growth, bloated, etc.).
2 male guppies
gray area on fins and possibly near mouth of 1 guppy
can't tell if it's a growth or just a discoloration, they won't stay still long enough, but it seems more like a growth
developed quickly, wasn't there this morning, quite noticeable this evening
their behavior hasn't changed at all

2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)? Please give exact values.
ammonia 0
nitrite 0
nitrate 5
temp 79
pH ?? hard to tell on the test I have, probably 8 or higher

3~ How large is the tank? How long has the tank been set up?
5 gallon hex
just finished fishless cycled and added fish 4 days ago
previously it contained a goldfish that didn't make it (ammonia level spiked)

4~What type of filtration are you using? Please give the name and number (i.e. Fluval 304) and amount of gph if known.
Marineland biowheel filter that came with the aquarium kit

5~How many fish are in the tank? What kinds of fish are they and what are their current sizes?
these 2 guppies are the only fish in the tank, 1 is full grown or nearly, one is pretty small

6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time?
5 days ago did massive water change after fishless cycle was complete, haven't done any since

7~How long have you had the fish? If the fish is new, how did you acclimate it/them?
4 days,
let bag float for 8-10min, added some tank water, let bag float for another 8-10min, netted fish and put in tank

8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.?
added a new plant right before I added the fish

9~What kind of food have you been feeding your fish, have you changed their diet recently?
feed a small amount 2x/day,
tetramin tropical flake food and twice we fed them freeze dried blood worms



Only other thing of note is that the little guppy chases the larger guppy quite a bit (could he be mistaking the larger male for a female? I'm certainly not an expert but it looks like he's trying to mate with the other male?). Could be causing stress to the larger guppy, but it's actually the smaller guppy (the chaser) that has more gray stuff on him, or maybe it's more noticeable because he's lighter... I don't know

 

[Zagz]

It sounds like it may be a bacterial infection. If you feel it is progressing quickly try using Jungle's fungus elliminator. It helps with fungus and bacterial infections. If you feel you have time you can try some melafix/pimafix, which is milder and better for your beneficial bacteria.

 

[nisi]

I suppose I owe an update...

It seems I was worrying over nothing. Apparently this isn't an illness at all. I watched the gray spots over the course of the next few days, and they come and go, sometimes within a matter of minutes. They vary from stark black when he's excited (in chase mode, at feeding time) to not visible at all when he's very calm. I never knew guppies could do that. It's been a week and he's perfectly fine (w/out meds), so I think I just have some kind of mutant chameleon guppy. Thanks for the help though, and I think I'll keep a bottle of Melafix around just in case.

 

[Zagz]

Well I am glad that your guppies are doing good. It's always a relief to have something go right.