Lost my male black Molly and now my orange male looks like he's dying!

[carla30]

Help needed! I am completely new to tropical fish keeping. We got our tank (35 litres) about 2 months ago. After some online reading and talking to our local pet shop, I tried a fishless cycle, adding a little bit of fish food every day to build up nitrates and amonia etc. I did this for one month. Then we bought our first fish - 4 Mollies (2 males / 2 females). Everything seemed perfect, fish looked healthy, active, always hungry and looking for food. A few weeks later we bought a group of 6 small neon tetras and 3 male guppies. I have been doing 30% water changes once and sometimes twice a week. Again, all fish seemed great. Then 2 days ago I came down in the morning to find my black male molly had died (he was my fav) Now today my orange male molly is lying on the bottom of the tank, not swimming, fins tucked in tight to his body. I fed them and he brightened up, swam about as normal eating, then about an hour later he is back to lying still on the stones again. Im afraid he's going to die like the black one did. All other fish seem fine and active. Not sure whats going on Any advice appreciated.

 

[fluttermoth]

Could you post the numbers from your most recent tests, please?

Do you know if you water is hard or soft?

 

[carla30]

Did a 30% water change again this morning and readings were ammonia 0.2mg/l, nitrite 0.1mg/l, nitrate 25-50mg/l, pH 7.9. I am actually not sure whether my water is soft or hard. I use AquaSafe water conditioner on the water before i put the fresh water in during a water change. I also put 1 AquaClear ball in the filter once a week. All the fish have seemed perfect up until these last couple of days. And im a little confused as to why whatever it is only seems to be affecting the male mollies. One of the females gave birth last week and even the few fry that didnt get eaten are still alive and active.
But again, this is all very new to me and I've probably made some beginner mistake.

 

[fluttermoth]

Any trace of ammonia or nitrite can affect fish; some are more sensitive than others, and fish can get worse over time when they've been exposed to them.

I would do some more water changes to get them both down to zero; it will not harm fish to do large or multiple water changes, as long as the new water is warmed and dechlorinated.

You can find out the hardness of your water on your supplier's website. You have a mixture of soft water fish (the neons) and hard water (the mollies and guppies), so one or other group isn't going to do well. Mollies in particular will not thrive in soft water.

I have to tell you that your little tank is very badly overstocked as well, I'm afraid. The mollies especially, can grow quite large (around three or four inches in length) and need to be in a much larger tank.