http://www.petsmart.com/product/ind...=LIghting+&+Hoods&f=PAD/psNotAvailInUS/No
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3733+13821+13823&pcatid=13823
Here are two bulbs. One is just a T5 and this is what is sometimes labeled T5NO.
It is the first one and it fits the Aqueon T5 fixture.
The second is a T5HO and its for T5HO fixtures.
Look at the details of the Watts on both. You will see that in the 18" the T5 is 14W.
You will see the T5HO in 18" is 18W.
BTW I have the True Lumen bulbs shown in my Odyssea 20" fixture cause the bulbs supplied/w it are not very good. They have a lot of glair.
The True Lumen bulbs shown give the best color I have ever seen in my tank.
The picture looks like the bulb is pink but the light from it is white.
In my opinion and from what I have heard also, the Odyssea has less powerful ballast than the better T5HO fixtures do. I know my light does not seem as bright as some T5HO fixtures that I have seen.
But if you have this on a ten g tank you WILL have algae with it.
Did you get the freshwater fixture ? Did it have two 6500K bulbs with it ? If it did, this is HO bulbs.