A lot of things seem to come up on the forums that are a result of recycled information that has been passed down through the years. I want to start this thread in hopes that this information will start to be widely accepted and known and hopefully dispell some of those "old hat" ways of thinking in the hobby. Some of these have mostly gone by the wayside and some are till in full swing and commonly believed in the hobby. Please feel free to add some of your own, add to my explanations, or even dispute my contributions.
1.) You should keep your PH at or between 7.8 and 8.3.
While those are acceptable levels this simply doesn't make a whole lot of sense. I've seen claims that the PH on Indonesian reefs (where most of the corals we keep will be found) is on average between 8.4 and 8.5. With readings often being higher and rarely below 8.0.
Conclusion: There is nothing to worry about if you PH is reading above the famed 8.3 mark. In fact, consider youself one of the lucky ones. If you're reading below 8.0 seriously consider betweer gas exchange and dripping kalkwasser to keep your PH higher in the acceptable range which should probably be more along the lines of 8.1-8.8. Maintaining a higher PH in closed aquaria is probably a good idea because of the greater amount of waste and acids that we encounter.
2.) Maintaining a KH of 8 is a good idea because it's close to what natural seawater is.
This one kind of goes along with the above suggestions. 8 dKH is perfectly acceptable, but it doesn't allow for a lot of wiggle room in out "dirty" aquariums. I've observed stress in various organisms when KH starts to drop much below 8. On the flipside there was a time when people commonly maintained a dKH as high as 18 in this hobby without any apparent stress from tank inhabitants.
Conclusion: While I wouldn't suggest striving for 18 dKH aiming for a little higher than natural seawater is a good idea because of the volatility of closed systems. I typically suggest people aim for 10-12 dKH. If you're using something that automatically replaces buffers in your system this is less crucial.
3.) 75-77 degrees is a good temperature for a reef tank or tropical fish only tank.
The majority of our corals come from corals and fish come from waters that range in temperature anywhere from 76-90 degrees with average temps in the low 80's. There are certainly creatures that are an exception such as those from Japan, Australia, and deeper waters which are more usesd to temperatures a little lower.
Conclusion: The old magic 76 degree mark has little merit and I'm not sure how it ever came to be in the first place. Maintaining temperatures in the low 80's is probably most natural and will suit most fish/coral available in the industry. Thankfully this has become more accepted in recent years.
4.) It's very important to keep temperatures stable.
This one pops up a lot on the forums. As you may have gathered from the above commentary, the temperature on your average reef isn't really stable at all. Temperatures can shift greatly with a simple shift of the tides or currents. There are also shifts between day and night that are close to 5 degrees on average.
Conclusion: Stop worrying about your daily swing in temperature from your lights heating the water. There's no need to go buy expensive chillers or controllers to always maintain the same temperature. In addition to being pretty natural the temperature swing may be good for your aquarium inhabitants and make them less likely to succumb should you have a more major temperature swing. In closed aquaria I wouldn't suggest testing the limits of this, but if your swings are under 5 degrees from day to night I wouldn't worry much.
5.) Any detectable amount of nitrates is bad in a reef aquarium.
While elevated levels are certainly a concern (20 ppm+) and I do feel it's best to maintain very low levels I think the toxicity of nitrates is highly exaggerated in this hobby.
Conclusion: If you're having problems zeroing out you nitrate tests don't fret too much. However, keep an eye on your nitrates levels and make sure they don't build up to levels that can start causing problems.
6.) Zoanthids are prefer low to moderate levels and flow, and they like dirty water.
As a group Zoanthids are very diverse. They can be found on the reef in pristine water conditions with incredible bright light and heavy flow. They can also be found at greater depths with lower light levels and less flow. Areas with turbid virtually stagnant water; check. Areas with huge waves crashing into them frequently being exposed to air, check. Dirtier water that may even be from sewage rinoff; check. Tidal pools with hugely varying conditions; check.
Conclusion: What's good for the goose may not be good for the gander. That's of course with the asumption that the goose and gander are both zoanthids. What the heck is a gander anyhow?
7.) SPS corals require huge amounts of light and flow.
Much like Zoanthids, SPS corals are a very diverse group. They are found at a wide range of depths in a wide range of conditions.
Conclusion: Just because you have an SPS coral does not mean it will appreciate being blasted with light and thousands of gallons of water per hour. Do a little research on your specific coral to get a better grasp of what conditions it might do best in. A good rule of thumb is that more delicate looking specimens come from areas with lower lighting and flow that would be experienced on the upper reef. More robust looking growth forms would probably appreciate being blasted with light and flow.
8.) The colors of corals are a result of the zooxanthellae which grows in their tissue.
While this is true to a degree, zooxanthellae is typically a shade of brown (think autumn colors). The bright colors often seen in photosynthetic organisms are the result of various proteins. Some of these colors are genetic, some are freak occurences that are related to light intensity levels.
Conclusion: A coral being brown isn't necessarily a bad thing, at least it has plenty of it's zooxanthellae symbiant. However, if you have ome crazy blue coral it is absolutely not because you have some freaky blue zooxanthellae growing in it.
Well, the site is about to go down for maintenance so I'll leave it at this for now. Please add to the list and discuss what I've posted thus far.
P.S. Sorry for any mistakes along the way in my typing and grammar. I blame the beers!