I've found that the only reliable heater I've had so far is the Tetra preset. Granted, it only keeps the water at 75/76 and only works on the smaller tanks, but at least it's constant...
Though tbh I'm getting pretty tired of constantly spending money on heaters, but I'll try the Theo out. Thanks.
Puck (Yellow koi HM king) / Scar (White HM) / Salt 'n Pepper (Silver HMPK) / 'That fish' (Copper butterfly HM) / No name (White DT) / No name 2 (Turquoise/white marble HM) / No name 3 (Lilac HM)
Bo Peep (Cambodian VT) / Goldilocks (Yellow VT) / Joie de Vivre (Multicolour VT) / Lil' Peep (Blue VT) / No name (Dalmatian VT) / No name 2