From my understanding from resources online, Nutrafin Cycle and API StressZyme DO NOT contain actual nitrifying bacteria (short form BB).

Actually, before nitrification can take place, we have overlooked an important process - 'mineralization' that has to occur before that. Mineralization refers to the breaking down of those wastes (such as fish waste) by certain strands of bacteria into ammonia. This production of ammonia can then lead to nitrification.
So if there isn't enough of these mineralization bacteria to breakdown the biological wastes to ammonia, nitrification will not kick start.

Overload of these biological wastes can in fact hinder nitrification, since the presence of these mineralization bacteria can create a hostile environment (and fight for oxygen etc) for the BB. A balance is needed.

Nutrafin Cycle and API StressZyme contain mostly such mineralization bacteria that help to break down the biological wastes into ammonia to kick start nitrification. If you look carefully at their product labels, they do not suggest any presence of BB, but only suggest they contain bacteria that aid the nitrogen cycle.

Fritz Lab has done some research regarding various brands of so-called 'nitrifying bacteria' and the report is shown in the link below.
http://www.fritzpet.com/article_comparing.html

Some extract:
" In truth, these products have little, if any, of the true nitrifying species of bacteria, Nitrosomonas (NS) and Nitrobacter (NB), which are found in Fritz-Zymes #7 & 9. What they do contain, primarily, are the same species of heterotrophic bacteria found in Fritz-Zyme #360. They produce enzymes that break down (degrade) the organic debris (sludge) and waste products produced in the aquarium. Most liquid type products contain little or none of the true nitrifiers. Instead, they rely on the ability of their product to maintain tolerable levels of ammonia and nitrite until naturally occurring NS and NB can become established. This could be a very long process considering the very slow reproductive rate of these two species.

Hagen, USA’s “CYCLE” and Aquatronics’ “BACTER ZYME I & II” are examples. They are equivalent to Fritz's Fritz-Zyme 360 Sludge Remover. They are excellent at degrading sludge and, under ideal conditions, will help control ammonia and nitrite levels. Tests showed that neither “CYCLE” or “BACTER ZYME” had any effect in reducing ammonia or nitrites in salt water.
"


So far, in Spore, the only product that states explicitly on their bottle that it contains real nitrifying bacteria is Fritz Zyme #7.
http://www.fritzpet.com/nitrifying_bacteria_lab.html

Another 2 excellent products that are proven are Fritz Zyme #360and BioSpira. They have a very short shelf life, and need to be refrigerated, and are costly. Hence, it is too costly to bring them into spore.

The various Fritz products and BioSpira receive very good reviews from users in US forums, but definitely not Cycle and StressZyme.


Another important fact to take note is that :
http://www.fritzpet.com/article_nitkeypoints.html

" There are no dry forms of any bacterial product that can contain viable Nitrosomonas and Nitrobacter cells. Unlike heterotrophs, they cannot form spores so they cannot survive any type of drying or freeze-drying process. "

So those dry pills or powder are DEFINTELY not nitrifying bacteria, simply because they do not exist in spores and cannot survive any drying process!
Just ask yourself, if BB can exist in dry form and form spores, then drying the matured bio material like biohome in the sun will not kill all the BB since there may be spores present in the biohome and can be activated when in water again?? No I seriously don't think so.

From my personal experience, Fritz Zyme #7 works great, and much faster than Nutrafin Cycle.

Hope this clears some air regarding products like Cycle, StressZyme and Fritz Zyme.
Some more extracts from the reports, if dont feel like reading them:
from http://www.bioconlabs.com/nitribactfacts.html

COLOUR AND SMELL
" The cells of nitrifying bacteria are reddish (Nitrosomonas) to brownish (Nitrobacter) in color. The solutions in bottles of Fritz-Zyme #7 and #9 are normally peach to rosy colored due to the natural colors of the bacterial cells and the proprietary solution used to keep them alive. What you see are actually clumps of bacteria stuck together by their own slime matrix.

Solutions of Fritz-Zyme normally have a musty stagnant water smell."

After reading this, I have stopped using the colourless, clumpless and smell-free Nutrafin Cycle. Even StressZyme has a pinkish colour, and has 'clumps' in the solution.


" Dry product formulations are by far the most common. These products consist of sludge removing and other nonpathogenic, heterotrophic species of bacteria and their culture media. Formulations may vary to some degree, but, they all perform the same functions. They all contain bacteria species that digest proteins, fats, oils, cellulose, and starch. These bacteria survive air drying by producing spores. NS and NB bacteria do not produce spores and are killed if dried. Dry cultures, therefore, do not contain any viable nitrifying bacteria. "

" They are largely non-motile and must colonize a surface (gravel, sand, synthetic biomedia, etc.) for optimum growth. They secrete a sticky slime matrix which they use to attach themselves. "

btw, from experience, as long as you have a big enough filter system, you can get away with not having a UV sterilizer.