Seizures And Crooked Backs

[graceofbass]

I have a 35 gallon hex tank with a Fluval filter that has been set up for 1 andd a half years. I haven't bought any new fish in about a year. There are:
2 neon tetras
1 rasbora
1 zebra danio
1 male betta
1 chinese algae eater
1 adult pregnant female dwarf sunset coral platy
about 15-20 platy fry

I haven't had any problems with fins being nipped, although some of the fish are somewhat territorial. Just to get that out of the way. Here's the problem:

I originally had 6 neon tetras. 3 of them got sick, 2 survived but had crooked backs. About 9 months ago while I was pregnant I had some kind of imbalance in the water and several of my fish died. I changed the water, got everything back to normal, and everything was fine, except my female platies started to swim in circles, upside down and would swirl around very quickly. All the adult females died, and only two of my fry survived to adulthood. I'm on the 3rd and 4th generation of my platies, and I have only one surviving adult. I also noticed that two of the fry have started to swim in circles, their bellies are also practically sunken in. Now my pregnant female, who has had several batches of fry without any problems, is starting to swim upside down occasionally, but corrects herself. I have been changing 30% of the water every week for the past 2 weeks. Any ideas on what the disease it? Should I just put them out of their misery and start over? If so, how do you disinfect a fish tank? Thanks.

 

[WILDER]

Need to look at your water stats in ammonia, nitrite, nitrate, and ph.
How often do you feed the fish.

First thing I want to rule out is neon tetra desease.
The spine can bend and the fish gets skinny.
But usually ntd start of as a bleaching of the red stripe area, or a mulky substance on the red stripe area.

Also check all fish for these signs.
What does it look like when the fish go to the toilet.
Is the anus enlarged or red and inflamed.

 

[graceofbass]

I am unable to test the chemical levels in the water because the chemicals used to do so aren't safe for children and I have a new baby. I do change the water regularly, and the water where I live tends to be hard.

The neon tetra is skinny and has a crooked back, but has been able to live with this condition for almost a year. I have not observed any stringy feces, or redness or swelling around the anus.

 

[WILDER]

Take a sample of your water to the lfs and ask them to write the readings down for you.

Also I would use an internal wormer on your fish.