Guppies getting sick :/

[bbestvin]

Hello everyone, I'm new to the website, but I've visited many times to view threads about aquariums etc. I really think this is a great community and thank you guys in advance for any advice you may share over the next few months/years.

To provide a background. I have a 10 gallon tank (in addition to a 20 and 16) that contains only Guppies. I set this tank up about 3 months ago, with two male Guppies and 4 females. The females would occasionally die without warning, and I determined it was a decoration using an air pump that was churning the water way too much and stressing the fish out.

I removed it and put in a stationary decoration and everything has been great since. I've had 2 males and 3 females with no issues for about a month and a half. Levels are all perfect, Ammonia/Nitrate/Nitrite are all at zero and I've been vacuuming gravel out occasionally.

Unfortuantely, with the onset of cooler weather, I realized my heater was not keeping up with the tank size anymore. It was an "automatic" adjustment one that's supposed to keep the water at 78. I know this isn't a good kind, but it hadn't caused any problems. I noticed the water had fallen down to 74-75 or so. In addition, one of the females started looking pale/white and her once flowy tail was stiff and rigid. She died, but the others looked fine. Fast forward to today. A pregnant female had 3 babies yesterday which I put in separate tank and I woke up this morning and she was dead. Now the others are either swimming at the top or having a hard time swimming. No signs of ICH, no fish rot as I can tell...no visible signs of disease. Could the pale/white fish have passed something to the others and can cold water cause fish to be prone to disease?

I appreciate any advice in advance!

 

[tamtam]

Welcome to the board!

Do you have this tank planted? Generally a cycled tank doesn't have 0 nitrate.

Anything that can cause your fish stress can make them more likely to get sick. So a rapid drop in temp, heavy current, poor water condition anything that can cause them stress.

Guppies though are generally pretty hardy and a temp of 74 or 75 is still well within their comfort range. Though if it was a fast drop it could have stressed her out enough.

I have a feeling that there is something else at play here but some more info would be helpful

What is your water change schedule like? How often do you gravel vac??
What do you use to test your water?
Did you cycle your tank before you got fish or did you do a fish in cycle?
What sort of aeration does this tank have?

Sorry for all the questions, it's just helpful when you have as much info as possible. It doesn't sound like sickness to me, I could be wrong but just from what you've said I think it's more of an environmental think.

 

[bbestvin]

Thanks for the welcome! Ok, I'll try to answer all the questions!

The tank doesn't have absolute zero nitrate, but it's somewhere in between 0 and 5ppm. I use the API Freshwater Master Test Kit to test the various levels.

The tank only has fake plants, nothing live. I try to change out the water once every two weeks, 30% water change. I use the gravel vac each time I do a water change to suck up any fallen fish food/waste/etc.

I cycled the tank before I put any fish in, and as I had mentioned, the fish that were in the tank were just doing just fine for the last month or so with no apparent issues. The tank doesn't have any air stones or anything like that, but a regular filter that breaks the surface to provide a good amount of oxygen in the water. Is there a way to test Oxygen levels that you've found helpful?

The other thing I've noticed, is that my blue guppy's tail has completely lost color. It used to be blue, and now it's 65% white....very weird.