guppies scratching? also plecos in tank, will medications harm them?

[Hybridfish7]

Just wondering why they're doing it.
I have a breeding trio of guppies in a 29 gallon and a 20 long. the ones in the 20 long are acting kinda off, but I can't see and parasites or anything on them. Sometimes the females scratch or swim with their fins kinda closed, but that's only occasional, they're still active and swim around normally, plus one's pretty gravid and at that aggressive point in her pregnancy. Regardless, I did a dose of metroplex for any parasites and furan-2 for any bacterial infections in the 20 long.
side note is it okay to dose those two together, also there's bristlenose plecos in there, are those gonna be okay? I didn't know some medications can harm plecos.
In the 29, I just saw my male scratch, first time I've seen him do that. Other than that that tank's perfectly fine, the females are acting normal.

 

[duanes]

Guppies can handle very brackish conditions (and many Plecos are somewhat salt tolerant too), if it were me, I would have used a salt solution 3.5lbs per 100 gallons, instead of tossing in meds, when I really didn't have a grasp of what the problem really is.

 

[Hybridfish7]

ah ok, now the question is how do I get the meds out
they stopped scratching now, so now I'm not sure how to get the meds out without emptying the tank

 

[duanes]

If you run some carbon in your filter for a day to 2, carbon will remove the meds.

 

[Hybridfish7]

problem with that is I have a sponge filter running in there

 

[Allan01230]

they have carbon attachments for sponge filters the old under gravel filters used to use them

 

[duanes]

You can hang a bag of carbon under the outflow of a filter, and it will do the same thing, or as do Allano1230 suggested.
What kind of filter is it?