When in doubt, there is a way to test a tank for its ability to process ammonia and not leave nitrite. Set up the tank just as you described. Then add ammonia to produce a max of 2 ppm. One easy way to do this is if you can find Dr. Tim's ammonium chloride which is formulated to produce 2 ppm if one adds 1 drop per gallon.
if you do not have access to this, then you need to find other ammonia and you need to know its strength % as well as the gals of water in the tank. You can them use an ammonia calculator to determine how much ammonia to add to produce 2 ppm in that amount of water. Dose that amount and then wait 24 hours and test for both ammonia and nitrite. Oddly enough, you do not need to see 0/0 for ammonia and nitrite to be able to add fish. In most tanks where we stock plecos the pH in not above 8.0. and the temp not much over 83F. Because it is only NH3 which will do serious harm to fish lets consider how much of a .25 ppm reading of total ammonia might be in the very toxic form: at that temp.
pH 7.0 = .0019 ppm
pH 7.5 = .0058 ppm
pH 8.0 = .0175 ppm
pH 8.5 = .0480 ppm
All the literature I have read indicates that almost no aquatic creature is at risk from a reading for NH3 of under .02 ppm and there is a red line at .05 ppm
*. So the odds are pretty good that it is only as ones pH approaches 8.5 that you need to really worry.
However, there are other factors to consider. First, we add ammonia to produce 2 ppm right away. In a going tank the fish produce ammonia all day long they do not du a single big dump. Second, in the presence of more ammonia than AOB can handle in 24 hours, they will multiply. How many more bacteria are needed in this example is pretty small if you have processed 1.75 ppm out of the 2 ppm added, you are roughly short 1/8 of the capacity you are targeting. The bacteria in this example will very rapidly reproduce to close that theoretical gap- it is a matter of a few hours. and don't forget that your plants are going to be helping a lot with ammonia. When plants use ammonia there is neither nitrite nor nitrate produced in tank water. So the plants usually mean a low ammonia reading will not be accompanied by a low nitrite reading as well.
So all you really need to do s a big water change before you add the fish. if you change only 50% of the water you reduce that .25 ppm by half which would mean even the 8.5 pH reading is almost at the absolutely safe line. BTW most of what is harmed at the lower .02+ levels of NH3 are "bugs" we do not have in tanks but do exist in the wild. most of the most sensitive fish are also not typical in tanks- think salmonids etc.
I have used this method for years when setting up a new tank in a hurry that I had to make fish safe. the most recent occasion was the 46 breeder sterbai corys I was given when I was expecting juveniles. I had to set up one 20 gal long tank for 19 fish. That was last Dec. 5th. All 19 fish are alive healthy and have been spawning regularly. I used the exact method described above with one change. I only had a single inadequate cycled filter and the plants available were slower grower so not the best ammonia eaters. I almost always keep a bottle of Dr. Tims bacteria in my fridge for emergencies, so I added some of the to the tank when I set it up. In less than 24 hours the fish went in despite a .25 ppm total ammonia reading on an API kit. I just changed the water as described and in went the overstock. When one adds bottled bacteria there is a balance between the capacity of the AOB and NOB right away, Whatever amount of ammonia they can handle they can also handle the level of nitrite that produces which is why seeding can have such a dramatic effect on cycling levels and times.
Imo, there is a realistic way to deal with nitrification issues and it is usually not what we read on many sites. Toxicity and danger are always situation specific and there is a bit more to it than gets discussed on many sites. Most will never tell you that chloride is a great way to deal with nitrite for protecting fish during a fish in cycle. That is because a water change does nothing to remove the nitrite already inside a fish, this takes 24 -48 hours to occur naturally and then only if no more nitrite is entering. And as long as there is any nitrite going into the fish, that time is extended. On the other hand, small amounts of chloride compete with nitrite to pass through the gills. The chloride will block the nitrite from entering. So when I use a tiny amount of salt to block nitrite into the water, I am actually helping the fish more safe than the person doing repeated water changes for many days to try and hold nitrite down. This method is allowing some lower level of nitrite to keep passing into the fish since N02 levels will continue to be created at some level until all the NOB have established to handle it.
All this said, darrel is absolutely correct that your tank as described is definitely fish safe based on the plants, added media and fish load. The above information is as for folks who are not sure their tank contains enough cycled media and plants to do the job for the desired stocking and want to know how they can tell. It also means one has to make the effort to use the methods described for assessing the situation.
* http://www.merckvetmanual.com/mvm/exoti ... #v23353508
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