Les alevins de guppy ne grandissent pas

My guppy fries are 8 weeks old and they still look like fries. Just that they've gained lil colour on their tail. I give them variety of food but once they like something they refuse to eat anything else. I have been feeding them harvested/frozen brine shrimp, blood worms, tubifex worms, and crushed guppy nutritional flakes. They used to love tubifex and brine shrimps. Half of them are also alway on the top of the tank. I have a airstone so the water is aerated. I also clean their tank every 2 to 3 days. But now they're not eating much. Should I be concerned? What else can I feed them for them to be healthy and grow faster.

I think you have a nitrite problem. Fishes are looking for more oxygen at the surface.
Test your water and if nitrite is positive, change half of the water without waiting a minute.
If you can't test, change half of the water. It won't do anything bad.

la meilleure nourriture est les nauplies d'artémias ou les micro vers vivant de préférence
Google traduction =
the best food is brine shrimp nauplii or preferably live micro worms.