You usually can tell between a bacteria bloom and a precipitation of salts ie... HCO3, Ca, Mg or K... If it occured as soon as you poured then it is likely a chemical reaction of which could be a handful of things. If it took a while to produce the white color and it was more of a haze / at the top of the tank then more likely a biologic reaction w/ bacteria.
From the sounds of it, more likely chemical. Most likely you somehow created an environment friendl to CaOH of CaCO3 formation causing a mass precipitation. Your heaters might show a light coating of the compounds over the next few days if this is correct.
