When preparing for bulb replacement in a T5HO light fixture, you can either purchase all of the bulbs at once and do a complete change of the bulbs, or you can change the bulbs one at a time. If you decide to change all of the bulbs at once, you’ll likely have to decrease the photoperiod (the length of time the bulbs are on) so that you don’t burn the corals. If you replace one or even a few bulbs at a time instead, the photoperiod doesn’t have to change. Additionally, changing out all of the bulbs at once can be quite expensive. At $20 per bulb, an 8-bulb fixture could set you back almost $200 if you factor in taxes and/or shipping. If you decide to change one bulb at a time, you could get away with one or two bulbs every few months which spreads the cost of the replacements out over a longer period of time. Of course with going this route, you have to keep track of which bulbs are new and which ones need to be replaced.