I think nutrition is going to play a big part in your fishes' growth rates as has already been mentioned. Some cichlids, such as those from Lake Malawi (your yellow lab) are omnivores, but 'lean' heavily towards being herbavores and should be fed accordingly, using meaty foods as a 'treat' one in a while (maybe once a week or so). Doing otherwise can cause problems for these fish because they lack the ability to deal with high amounts of proteins and such. While it is usually not our first concern, chosing fish with similar diets may be something to consider when stocking a tank. Likewise, stocking fish from a similar region, or in the case of african cichlids, the same lake, is often suggested as well...even though I know a lot of us do not follow that guideline all that closely.
Frontosa, from what I have just read seem to have a debatable diet...one website says they are also very herbavorious, and another says that their teeth are shaped in a way which suggests that they are carnivores. Yet another website says that when wild caught versions are disected, their stomachs contain other cichlids from the family
Cyprichromis . So, the nutritional needs of these fish is still a mystery to me. Howver, all of those websites state that they are very 'lethargic' fish (meaning they dont want to expend a lot of energy all the time) and that they are usually found in deep waters, with similar, slow moving fish. Hence, it might be possible for them to be stressed by a lot of activity. I have also heard that these fish may be an exception to the 'freshwater fish can acclimate well to a wide range of pH levels' becuase of their habits of living in deep water. So, apparently the 'target' range of pH would be higher than 8.0, but no less than 7.8...or so I have just read.
Lastly, a nitrate level of 0 to 0.5 is not really all that 'normal' and I would take a closer look at that test kit. While there are exeptions (e.g. planted tanks, those with special filters, etc...), nitrate levels with build up over time and we would remove them via water changes. Also, in a cycled tank, even a nitrite level of 0.05 ppm would be a sign of trouble. If you would like, check out the freshwater cycling article in FTF's article section which you can find quickly by clicking
HERE. It may help clear up any confusion as to what you would like to see from your test results during 'normal' conditions.
=========================
By the way...after searching for one of my pictures for use in another post, I ran across this one below which shows just how large your tinfoil barb could grow to...IMHO, it makes an 82 gallon tank look a little bit small, especially if you consider that they are probably best off in groups of three or more.
like 1-2 inch big one 5 inch, and the sucker fish wich should be the fastest growing has only grown 1/2 inch around, how long should it take for all these fish to get large? 
