Bettas keep getting sick

[Coraline22002]

My second Betta just got sick and is going to die.  I got her in November and she has been fine up until the last couple of weeks. She had a white string hanging from her stomach and I treated my tank with Prazi Pro since it appeared to be worms.  She also had a gill that looked like it had hyperplasia with a little white in it. Once I treated with the Orazi Pro it looked better.  A little over a week ago she stopped eating and became really lethargic. I noticed another string and the white in her gill again and she started letting the filter suck her in so she'd stay at the top.   I've included a picture here to show the white cottony ball coming out of her gill. I started treating with Maracyn 2 but she's too far gone. The same thing happened to my last fish after I moved into my new rental last summer.   We are on the same water source but it has a water softener  

water parameters are as follows:  ph 8.5, ammonia 0, nitrites 0, nitrates 5 ppm, kH 300 and gh 0-30 ppm  my tank has five plants in it  and a steady 78 degrees  

I talked to the local fish store about how high my ph is and they suggested mixing tap with RO 50/50. I started doing that a few weeks ago, which is the only difference I can come up with. The RO hasn't managed to change much so there isn't a huge shift in parameters. 
 Since this is the second fish, I don't know if I should not get any more fish until I move or if anyone has suggestions for this issue. I'm so frustrated.  Both fish have survived about four months. I check water constantly and clean my tank every week. 
Please help!

[ndfi78]

I don't have an answer for you, but I did want to say I'm sorry it is happening. 

[Coraline22002]

Thank you!  I'm going to try using potassium pellets in my water softener and see if that helps. I think the salt in the sodium pellets is bad for them. 

[Colu]

Looks like saprolegniasis  infection ick x and maracyn together are a good combination to treat saprolegniasis if your getting reoccurring fungal problems it's usually caused by poor water quality bad diet or stress weaken the immune system making them more susceptible to infection what you need to is go don't the list it's a process of elimination are you using water dechlorinator like prime when doing water changes how often are you feeding and what are you feeding any resent edition to the tank  what type of filter are you using do have an air stone as low levels of desolved oxygen can stress fish out