Cremecicle Lyratail Mollie

Question
I have a 10 gallon fish tank with 4 mollies. One black male one black white spotted female one white black spotted femal and one cremecicle female. So we have 4 fish total and have 3 babies as well. We did are completewater change last night and let the water sit and checked all the levels. Ph was at 7.0 nitrates were good and ammonia level was safe. This morning when I woke up there was a spiderweb like white substance all over the inside of our tank. I noticed it was coming from our orange cremecicle mollie. She is still excreting this substance and our black male fish has now died! What is this substance she is secreting? Is it going to kill the rest of our fish? Is this fish having babies now? Please let me know asap! This is our first time having fish and don't know what we need to do with this situation.
Thank you so much,
Angel

Answer
Hi Angel;

Fish have a natural protective slime coating all over their bodies. When they are stressed, it goes into overdrive. Changing so much water all at once has put them all into shock. Even when the temperature, pH, ammonia, etc, is the same as what they are used to, there are other elements we can't test for at home that we can't see so something wasn't the same as before and it has stressed them. The best you can do is wait it out and hope that the rest recover. Or, perhaps you forgot to use a water conditioner? If you didn't, add some now.

All tanks need a weekly water change of no more than 25%. Vacuum the gravel at the same time. Leave the fish in the tank to make water changes. It is less stressful to them if they can just hide and you just slowly work around them. Weekly 25% changes keep the water quality and water chemistry more consistent. Make sure the new water is the same temperature as the old water and add a water conditioner every time.  

I hope the rest do okay...

At Your Service;
Chris Robbins