guppy help

Question
hi, i have a 16 litre tank with 3 guppies 2 boys and 1 female also in the same tank 2 gold fish and a bristlenose catfish.
i think my female guppy is pregnant because she has a gravid spot is this true about the gravid spot?
also if she is pregnant she would have to be about 3 weeks in to pregnancy, she still eats and i have heard that they dont eat when they are pregnant is this the case?
she is getting fatter but she is not looking like she is going to explode she just looks like she has gained a little bit but her gills protrude a little forward from the little extra weight
how will i know when to put her in the floating breeder box can i put her in there now?
i dont know how she is pregnant she attackes every fish severely except the bristlenose, the orange gold fish is missing heaps of scales because she is for ever bitting him, is this aggression because of being pregnant?
i have also heard that the hide when ready to have babies she does not do this and swims all over the tank fine with no struggle. i have only had her for about a month.
also i forgot to ask but i think my bristlenose has ich and im treating the tank at the moment with science products white spot at half the normal dose will this harm mum and unborn fry.
any answers would be much appreciated thankyou
do you know much about bristlenose catfish?

Answer
Mel:
The gravid spot is will grow large and darken over time. It is a simple myth that the pregnant guppies do not eat during pregnancy. Don't put her in the breeder box until you notice abnormal behavior like pacing up and down the sides of the tank, the fish becomes very bright or vibrant, or hiding beneath ornaments or plants. The female will gravitate towards the heater when she is ready to give birth. If you put the fish in the breeder box, and she doesn't deliver for 24 hours, release her back into the main tank. Aggression is normal for pregnant fish-- Do you have goldfish and guppies mixed together??
Bristlenose catifish like water with lots of movement/oxygen(river) and lots of nooks and crannies to hide in and suck algae. They are most active when the sun goes down and then the sun comes up. They do not like unwanted guests, like other fish, and they will definitely find a genius way to get the other fish out of their territory. They like to rest upside down. Don't mix them with aggressive, territorial fish. Good luck and ask a follow-up if needed!!
-Jenny