Mollies dying

Question
I have a 10 gallon tank that has been running about 2 years. We had goldfish until 2 months ago when we switched to tropical fish after the goldfish died. I started with 3 small male Dalmation mollies who stated dying off one by one after 3 to 4 weeks. They had no visible lesions just started swimming more slowly and seemed to droop their tails. They would hide in the plants or swim in place by the heater. After a few days of this they just lay on the gravel and died within a few hours. After the first male died we got 4 new female mollies (black, silver and Dalmation.) The very small silver molly died in the same way after 2 weeks. The black molly then had 8 babies who all died within a week. They were not eaten but simply lay in the gravel and died too. I then treated 5 days with Maracin 2 because the other silver molly was starting to look weaker and hide. She died several days after the treatment was finished. The Dalmation molly is now looking weaker as well. I am so frustrated by this. My water has always checked out ok and I am checking it several times a week. I have had problems with high nitrates in the past which probably did in the goldfish but have been doing weekly 25% water changes since. Nitrate levels have been 10-20 ppm. Ammonia has remained low <0.5 and nitites always negative. The ph is 7.5. Temp is 76-78. I started with 1 Tablespoon of aquarium salt per 10 gallons but have added 1.5 tsp to the last two 2.5 gallon water changes. I really think this is a disease rather than just stressed fish. We also have a tiny guppy baby who was a stowaway in the pet store bag. It seems to be thriving so far. Any idea what I can do to keep my last two mollies alive?

Answer
Hi Colston;

Since the guppy is doing okay I would suspect some bad batches of mollies from your local fish stores. Many stores in the same area will get fish from the same wholesaler too, so it may not help to shop at another nearby store. There are certain times of the year when different types of fish just don't do well too.

Maybe they are too cold or caught a chill before you even got them. Mollies like their water at 78f or 80f. They also need veggies in their diet as well as frozen brine shrimp. Give them bits of spinach, spirulina alage, zucchini and cucumber chunks, and romaine lettuce. These things should be fed at least 3 times a week and flake food the rest of the time.

The tank is kind of small for mollies too. They get at least 3 or 4 inches long each and are much better off in a 20 gallon or larger. You might want to try a different kind of fish and see what happens. Maybe some platies or tetras. Avoid swordtails though. They get even bigger than mollies.

Have you tried to alter the pH with chemicals? If you have been, don't do it anymore. This only causes fluctuations which is much more harmful to the fish than letting them get used to the pH your tank tends to be. What they really need is fresh water and a good diet. Your weekly changes are great. Keep up the good work.

At Your Service;
Chris Robbins