How to include random variables in the formula

[PaulaEterovick]

Dear @gibsramen and @mortonjt,

I built a formula to look for the effects of two variables likely affecting tadpole gut microbiome: temperature (with 5 levels) and nitrate concentration (with three levels), but I also have two random variables (aquarium and PCRreplicate) that I don't know how to include as random variables. I see you included random variables in your model in the original BIRDMAn paper, but I couldn't find the formula anywhere (sorry if I missed it).

This is my formula at the moment (without the random variables):

formula="C(Temperature, Diff, levels=['18C', '22C', '26C', '28C', 'Fluctuating'])*C(Nitrate, Diff, levels=['control','N50','N100'])"

Thank you very much for the availability to help Paula