I can attempt to explain some of my experiences with this. Please see below.
OK:
So not to highjack the OP's thread. But I am interested in this - in fact my 30 gal QT is still sitting dry downstairs after a year because I haven't had the heart to go down and tear it down after so much frustration with it - if I can use it to good effect again - for my QT needs then I would do so. My experience though (a year and a half ago) was that
1) I had a sponge from the sump in there and another on a HOB filter with floss to catch food particles.
This is common practice as it helps to "cycle" the QT as the sponge acts as the biological filter when placed in QT (I do it as well). In my experience, the #1 killer in QT is ammonia build up from a non proper QT cycle.
2) Foxface - problems I had was that nitrates would raise quickly. I was doing water changes in the 25 to 50% range twice a week to keep it below 5. Which meant that with those large water changes I was struggling to keep temp and pH stable. I had to do water tests like every other day to keep on top of the ammonia/nitrates - VERY time consuming. I was told it ultimately died because they are "messy eaters" and shouldn't be QT'd.
You shouldn't be worried about nitrates or nitrites in QT at all. My nitrates have been around 100 before for 5 or 6 weeks (I got lazy and didn't do any WC's the entire 10 week QT regimen) lol. Again, you want to monitor ammonia.
2) Second try with foxface - someone suggested AmQuel to manage ammonia and limit nitrates going up. Someone later told me that even with an airstone this likely killed him because it used up oxygen in the tank.
I doubt this was the issue, personally. I have also used Prime to help if I see any ammonia build up (does the same as AmQuel). One thing about AmQuel and Prime, however, is that it does NOT mix with any type of copper at all! It will turn the copper into a toxic form and will kill the fish if used in conjunction.
3) The yellow headed sleeper gobi and the orange spot both died with red bruising on their face. I was told that these shouldn't be QT'd because they need substrate and they died from infection secondary to damage to their mouth from banging.
Grab a piece of tupperware and put some sand in it. I did this for my melanarus wrasse. He dove in it and slept every night in the sand in the piece of tupperware. The QT was still BB.
4) The Banggaii and the chromis - I was told these needed to be added together as a group - but then in each case (two separate times) again the nitrates got high, large water change issues, and in-fighting left me after weeks of QT left me with one sick beat up cardinal and the other time with 1/2 the chromis I started with.
Again, I personally wouldn't worry too much about nitrates in QT. Large water changes in QT have also led to issues with me in the past; therefore, I only try to do small 20% WC's. The only time I would do a large WC in QT is if ammonia was present.
5) The angel fish I was told not to QT because 30 gal isn't big enough and you can't treat because of copper sensitivity issues anyway.
30 gal should be fine to QT most of the hobby angels you can buy. Many angels are, however, sensitive to copper. You can perform the observe technique (just watch to see if the fish gets ich or something), or you can prophylactically treat by using tank transfer or hypo if you wish to treat for ich.
On another note, I have used a low dose of copper (cupramine) on a copperband (.35 ppm instead of the suggested .5 ppm). I have heard from others that around .3-.35 usually works even on fish that are sensitive to copper. .3 ppm copper is enough to take care of the ich.
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Finally - after MONTHs with virtually no fish in the tank - I was convinced to just put the fish into the main DT. The fish I added have continued to live, I've since added several new fish.
You have been having good luck. You are always taking a chance imo. I've gone through ich in the DT once and I've also had a bout of uronema that 3 fish came down with in QT. The entire DT would've been wiped had I not QT'ed them.
Please understand - I'm not insensitive to the fish that I'm caring for and these experiences trying to QT nearly drove me out of the hobby before I even got the first fish to the DT. If I can do it right - I will, but I started to get the feeling my QT was more like the "tank of death."
I totally understand. QT is definitely a hastle, but I personally don't trust anywhere I buy fish. I would rather treat them myself to try to contain and omit any diseases that could arise in the DT which I have invested 1k's in.
