"Are the cascading pools, Hidalgo (?) a day trip from Mex City? "
Tolantongo is 200 kilometers/120 miles north of Mexico City so people driving private vehicles or riding in special excursion buses can reasonably expect it to take four hours to get there and another four to return.Taking public transportation adds a bit more time to the journey. For that figure 4 1/2 hours each way.
Most visitors to Tolantongo are domestic rather than international tourists. To avoid having to pay for lodging at Tolantongo some Mexico City residents make lengthy (and probably exhausting) day visits there. But, I recommend instead making that excursion (visiting Tolantongo and also its gateway town, Ixmiquilpan) a two day or two-and-a- half-day venture. For a day trip pick instead a balneario or other rustic location that is closer to Mexico City.
Mclarjh has mentioned a waterfall at Rio Frio de Juarez. I've not been there, but it may be worth learning about.
One afternoon many years ago I enjoyed floating in an intertube down a clear cold water spring beside attractive tropical vegetation. That was at "Las Estacas" about two hours south of Mexico City in the State of Morelos.
But, judging from their web site, Las Estacas no longer offers "tubing" and has become an upscale spa.. Both their daily admission (335 pesos ) and lodging costs (1,700 to 4,300 pesos for a room or suite) are high, compared to other Mexican balnearios.
https://lasestacas.com/