Possible internal parasites? - Clown

[Au_ThatHurt]

Hey everyone. So I have had these two clowns for a year now and I had gotten them from a person quitting the hobby who had them for 2 years. I have not added anything new to the tank and the previous owner just added a blue damsel who doesn't seem to have an issue seen as white stringy poop on the female clown. I have noticed my female clown expelling some long, stringy, white poop before, but whatever the cause, it does not seem to affect diet or energy levels.

My question is could my clown have been living with these internal parasites for years or could it just be from a high protein diet found in the pellets I have been feeding. I feed mysis or brine shrimp every 4 or 5 days or so but aside from those days they seem to enjoy the pellets and flake mixture I feed just fine. The other clown does not seem to have any white stringy feces and the blue damsel does not have irregular feces (I assume they would have "caught" by now.) There are only these three fish in the tank fyi.

Thanks!

[Au_ThatHurt]

1. How old is this aquarium?
1 year under my care, 2 under previous owner

2. If less than six months old, what is ammonia level?
ammonia @ 0

3. What is SG of this aquarium? How measured?
1.024 (refractometer)

4. When was the last fish added to this aquarium?
over a year at the very least

5. Was it quarantined? If so, how? And how long? Was it prophylactically treated? How?
previously quarantined for 72 days w/ copper treatment after getting from previous owner (suspected ich)

6. If you are using a copper based medication, which one? How often do you measure level? When?
copper treatment was about 8 months ago and would not need to for internal parasites I presume

7. If you are using hyposalinity, how did you calibrate your refractometer?
N/A

8. Please describe in detail, the appearance of the fish? If there is one or more pimples, are they lumpy? What color?
N/A

9. Please describe the behavior of the fish as best you can. Is it acting reclusive? Is it always up towards the top of the aquarium? Is it avoiding light? How active is the fish?
Very active and swimming around the entire tank with the other mated clown. Swimming at the top and bottom.

10. Is the fish eating? What?
Yes, eating normally although had to feed mysis today because I believe she grew tired of the pellets. Normally just feed brine and mysis whenever they seem to be growing old of the pellets and then the next day they are back to the pellets for a few days until the same boredom occurs.