my pregnant molly, and pregnant guppies gravid spots

Question
tank size- 55gl.
number of fish- 22 assorted fish. almost half are prepubescent guppy.
types- guppy, red tetra, black molly, lyre molly, rainbow shark (only while he is young), platy, pleco's, and one cory.

i have a gold lyretail molly who has been pregnant for about 2 weeks. she is mature enough for a few births. she is also huge! she stays at the bottom of the tank, and only moves her mouth and gills. i honestly don't know a stitch really about chem. levels. im a beginer in a sense.
nitrate-160
nitrite-1.0
hardness/gh- 90
alkalinity-30
ph-6.2

current temp- 73
i do about a 15% water change every week and a half or so.
i do noy gravel vacuum.

what do you think is wrong.
for my guppies, what color should a non pregnant guppies gravid spot be? what color should a pregnant guppies gravid spot be. what does a color changing gravid spot mean?
thanks alot


Answer
Griff: Your tank is toxic.  You need to do a 30% water change today and then a 20% tomorrow.  You need to clean your gravel with a gravel vacuum and you will need to do 20% water changes on a weekly basis and change the filter media every 30 days.  Right now  your nitrites are high enough to kill your fish.  I am afraid to ask what your ammonia levels are... so some tank maintenance and get back to me with the new water chemistry levels.  It sounds also like your gold lyretail molly is about to have babies... be careful when you clean the tank that you do not suck them up.  If it were me I would go to the nearest pet store and buy a handful of snails to help with your tank cleaning.  You are also going to have to be prepared to feed baby fish... first bites is a good brand of fry food.... dave