Can guppy deaths affect bns?

About 10 guppies out of 20 disappear in a few days last week.
I had no idea what happened to them but today I found a dead female.

My peppermint bns and goldfish look fine. Could the guppies have a sickness that the bns could contract?
Thanks, I have no idea what I should do T_T

I don't have any ammonia or nitrate testers either, but I assume that the catfish would drop off before the guppies if it was something to do with that.

http://www.bristlenoseworld.com/t2961-important-read-before-posting-template-inside

Mixing tropicals with coldwater fish (i.e. Goldfish) is never a good idea. You can't possibly meet either of their needs as long as they are housed together. It's quite possible the goldfish ate the guppies. I would suggest putting the Goldfish in a different tank and keeping the BN's and guppies together. I'm also a huge advocate of water testing. How long has your tank been set up ? How big is it ? Those are also important questions. BN's contirbute heavily to the bioload in a fish tank but Goldfish are even worse. Hope this helps.

My dad bought the goldfish and i have no where else they'll fit. The tank heater is on 21 degrees celcius, I tried to get a medium between tropical and coldwater.
I've had the tank set up for a year and it's 170 litres. I've got a sponge filter and a canister filter (I don't have the boxes anymore and it doesn't say what it's called) that apparently is more filtration than I need. I'm trying to sell the goldfish at the moment anyway.
I was just curious to see if there may be a simple reason why the guppies died, but everything seems to be fine now anyway.
Thanks