white poo

Hi all! I'm new to forums but I joined this one because I'm concerned about my betta. I got her at the beginning of March as a surprise gift. I've done extensive research and tried to give her the best care I can. I honestly can't believe how attached I've become She's a feisty, flitty little...

Is my guppy ill ? It has had this white stuff (see picture ) dangling from him for about 3 days . Our tank has readings of nitrite 0.5 , ammonia less than 0.02 , our ph is 6.8 and our tank temperature is 23 degrees Celsius. We do water changes twice a week . If it has an illness can you please...