Pregnant Molly/shaking/unable To Swim?

[EvilCupcake]

Hi there!

I'm new here but have a question, if any of you are able to help that'd be wonderful.

I've just exchanged a male dalmation molly to a female today (we had three females, one male, really didn't want lots of fry every month!) she appears to be pregnant but since being in the tank hasn't been able to swim upwards at all. When she tries to, she shakes and nearly goes onto her back, she just appears to not be able to do it!

Oddly enough, the other mollies seem to be doing the same? I've just seen the other dalmation molly try and swim upwards and basically shake like crazy. Along with a silver molly who's back has become very arched and does a 'wobbly swim'?

I'm pretty new to fish keeping, it's just slightly alarming to see and would just like to know if more so with the pregnant new molly that she isn't going to drop dead on me suddenly?

Thank you in advance

 

[OldMan47]

Welcome to our forum Cupcake.
You are describing a condition that is often seen in a molly that is asked to live in water that is too pure, meaning very few minerals.
A molly is not a fish well adapted to living in ultrapure water, the kind the South American cichlids and tetras like. They do best in semi-hard water with a typically high pH of over 7.5. A lot of the possible actions for that depend on what is in the tank with them. If you have sensitive "soft water" fish in the tank, the cure means first establishing a separate tank so that helping the mollies does not mean damaging the sensitive fish. If you have all common livebearers with maybe a few of the tougher and more versatile egg layers like paleatus cories or even angels, the solution is simpler. If you have very soft tap water you could simply add some crushed coral or crushed shell to the filter flow path to increase the KH, GH and pH of the water and thus improve the health of the fish. If you have filled the tank with bottled water or RO water, as far too many people do these days, change over to straight tap water by doing a 20% daily water change for a week or so. Tap water often has plenty of minerals for typical molly needs and is acceptable for most other fish.