Originally Posted by smota
My tank size is 75 gallon. My filtration is a professional eheim wet dry canister and I also have the coralife protein skimmer up to 220 gallons. I am currently treating this tank with copper for ich, but all the levels seem to be okay - levels of copper (0.15) and levels for ph (8.2), amonia (0), nitrites (0), nitrates (5).
I don't understand it because if the water condition is perfect... why are my fish stressed? why are they getting ich?
Ok, this may be a long answer, so i apologize ahead of time. Your question is the same type of question that many converted Freshwater hobbyists ask early on in the marine hobby. In Freshwater you are told to do a number of things to keep your tank healthy, but in the real world we skip most of these things. We don't really test for Nitrite and Nitrate. We don't really change 20% of the water EVERY week. And we don't really limit ourselves to the number of fish we are told. We push the limits, and everything works out fine.
Unfortunately this concept can not be applied to the marine hobby in any way. In my opinion, having Freshwater experience makes the marine hobby more difficult, because NOTHING from a Freshwater tank applies in the marine system.
Moving on.... The next problem is the pet shop. They can't scare their customers away from the marine hobby or they will not make money. So, they tell their customers what MIGHT work, rather than what actually DOES work. Protein Skimmers are presented as optional pieces of equipment that can be overcome with more frequent water changes. (not)
The UV Sterilizer is hardly mentioned, despite the incredible benefits and disease prevention. Quarantine tanks are almost never sold, because human nature would never allow a fish to be quarantined for 3 weeks prior to the next fish purchase.
In other words, new marine hobbyists have everything going against them. The information they are given is poor and human nature is not on their side. Simple mistakes are made that are so easy to prevent, but they have no idea they are making a mistake and the pet shop is no help.
For example, you gave a pH reading without an Alkalinity reading. Unfortunately your pH reading can not be interpreted without knowing Alkalinity. It is useless. I suspect pH is a huge part of your problem, based on the description of your fish. I also suspect you are not using any type of buffer, because you don't mention it. You need to purchase a buffer and an alkalinity test kit. I like Kent Marine Super Buffer DKH, but there are many to choose from.
You also listed your filtration choice with pride, but personally i would never consider the option you are using. Why? Because your biological filter is separate from your protein skimmer. The positive benefits of the protein skimmer are negated by the constant biological activity resulting in Nitrate buildup. Your skimmers function is to remove organic acids prior to their being broken down into Nitrate and effectively removing carbonates from your buffer system. The wet dry function is to break down organics into Nitrates, utilizing carbonates in this process. These two filters do not compliment one another. They are opposites. The wet dry needs to go and live rock needs to be used in its place, along with FOUR INCHES (not less) of aragonite sand.
Next, lets talk fish selection. These fish choices are horrible. I really really dislike your pet shop. The Purple Tang is a Zebrasoma genus and will only thrive in a very seasoned aquarium with a lot of algae for grazing. It is extremely aggressive and should be introduced as the last fish to a community and should never be kept with other Tangs in a small tank. Yes, a 75 gallon is small by marine standards. This fish also grows larger than your tank will allow. Tangs grow 75% of their adult size within the first 12 months of their life. You do not have time to "upgrade". The damage will be done very quickly to this fishes development.
The Powder Brown Tang also fits the description listed above, but it is an Acanthurus genus, which means that it grows even larger and needs even more swimming space. It is also one of the most sensitive Tangs sold in the aquarium trade and should only be purchased by very experienced hobbyists. I personally would not buy this fish using your money, much less my hard earned dollar.
As to the water tests. You list Ammonia, Nitrite, Nitrate, and pH as being the standards of water quality. These just happen to be the 4 most common things we test in the aquarium, but they are not by any means the only method of determining an aquariums health. The fact that your fish are behaving in this manner tells me that something is seriously wrong with the water quality. There are endless chemical reactions going on in the marine aquarium. The reason we use live rock, live sand, and a protein skimmer is to help stabilize the environment. The continuous use of a biological filter will contribute to a continuous change in the environment. Here is a link http://www.reefkeeping.com/issues/past.php
to a great internet based magazine. You will have to scan the past issues, but there is an article which goes into detail on several dozen of these other reactions that effect our aquarium environments, none of which we have adequate tests for in the hobby.
Finally, i have to preach infinite patience. You have to pretend that you are shopping for a used car. Walk away from 90% of the livestock purchases you consider making. There is almost always a reason NOT to buy the animal you are considering. Be extremely picky. Buy only hardy fish that will fit in your aquarium comfortably as an adult. Buy only fish that are feeding well and well acclimated to the dealers tanks. And most importantly, never buy a fish that you have not researched on your own prior to purchase.