Time to invest in a tankless water heater!
Don't know what I would do without mine.
I try to do them every 1-2 weeks and will usually do 2-3 tanks in one day... Of course, I have 10 tanks, but more than half of them are 20 gallons or less.
Sometimes I dread changing the 150, not because it's a lot of work, but because it means the plecos will spawn again and I am out of places to put baby plecos.