The guppy is a female, as can be seen by the anal (bottom) fin, which is fan or triangular shaped in females and long and straight in males.
She has gill flukes but that is not causing the white stringy stuff.
Is the white stuff coming from the fish's butt or from the fin?
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The pH is a tiny bit too low for livebearers (guppies, platies, swordtails, mollies) who need a pH of 7.0 and above. They also require a general hardness (GH) of 200+ppm (250+ppm for mollies).
The GH can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
The pH and GH is not causing the problem.
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If the stringy white stuff is coming from the fish's butt, and the fish is still eating well, then it probably has intestinal worms.
If the fish is no longer eating then it could have an internal bacterial or protozoan infection.
Is the fish still eating normally?