Actually ATI bulbs are cheaper. I order mine from bulkreefsupply.com. 39W are only $19.99 and even cheaper if you have preferred customer status. You do have to take shipping into account but I usually do a large order every year so shipping doesn't affect price too much. I used to use Giesmann equivalents (Giesmann Actinic+ = ATI aquablue+, Giesmann Aquablue = ATI Aquablue special) but they were costing me ~$25 each locally and they have lower PAR than the ATI bulbs.
|