In a tropical fish tank what are acceptale levels of
NO3
NO2
GH
KH
ph

tropical and cold water all levels acceptable are the same,the only difference being the temperature-

NO3 (nitrate) <40ppm (more than this and water change)

NO2 (nitrite) 0 (zero means you are cycled, never allow it to come about 0.25 during cycling as it will damage your fishes gills)

GH and KH i have no idea, i have never worried about them.

Ph varies, mine is 7.5 from the tap, and i never ever add anything to change it and never would, it is far better for the fishes health to acclimatise to your tap water ph than have you add anything to the water to try to change it, and them having the possiblity of Ph swings. it is more important that the Ph is stable than it being a certain number.

the other one you missed out on was ammonia (NH3 NH4) and this should also be 0, this is the first step in the cycle process, and any reading means you need to do a water change as ammonia will also burn the fishes gills, unless you are fishless cycling your aquarium in which case it should be left to allow the nitrifying bacteria to colonise your tank and feed off of it.

cycling your aquarium is a must, without seeding a tank from an already established tank this should take approx 6-8 weeks,can be dropped to as little as 2 weeks if you use a handful of seeded gravel/filter media from an up and running tank. when readings of ammonia and nitrite drop to 0 and nitrates start to climb you know you are cycled.

basically, cycling is where fish produce ammonia (harmful/deadly to fish)from poop/breathing, bacteria grow to change ammonia into nitrite (also harmful/deadly to fish), then bacteria grow to change nitrite into nitrate (harmful over 40ppm approx, water changes should be carried out to remove excess nitrates and bring levels down to levels less than 40ppm) the only way to take nitrates from the water is to change the water.

ammonia (harmful/deadly)> nitrites (harmful/deadly)> nitrates (harmful over 40ppm)

without ammonia in your tank your bacteria will die off from starvation so if you have no fish in your tank you can cycle it by feeding the tank as if you had fish in there. never turn off your filters apart from when doing maintanence as the bacteria colony in your filter media will die off without a supply of oxygenated water to them. chlorine in tap water will also kill off your bacteria, always use dechlorinator before any new water is added to the tank.

Haven't a clue what my readings are as I've never ever done any kind of water test in over 30 years of fishkeeping and rarely lose fish apart from with old age. I use water conditioner when performing partial water changes. Never cycled a tank either. I set up the tank then put fish later that day or next day. My LFS dealer, who is a personal friend, advises people to do that, but not many fish and gradually add them. I've seen him sell the tank, equipment and fish all together! Fish-in cycling I believe it is then. If people want to take weeks doing fishless cycling whilst staring at an empty tank then it's up to them. Not saying it's wrong but I haven't the patience.

both fish-in and fish-less cycling will take around 6 weeks, to allow the bacteria to colonise the filter media and substrate. i would never even consider buying a fish from a dealer who will sell both the tank and fish in the same day terrible idea! even pets at home dont sell tank adn fish at the same time!

it takes some time to set-up a tank from scratch, those poor fish he irresponsibly sells at the same time as the tank have to sit in that little plastic bag, before being put through the trauma of being left in an uncycled tank with ammonia and nitrites burning their gills, im guessing he wont explain the cycle process if hes dumb enough to sell everything at the same time, so the new owner wont have a clue.

i wonder why so many people give up on this hobby bad aquatics stores with bad knowledge, and typical 'do anything for the sale' mentality.

oh and just because you have been in the hobby for 30 years doesnt mean you know everything, things change and new knowledge and new products means things can change in the way people do things. please dont encourage people to put their pets through the trauma of not cycling and not paying attention to water parameters, its cruelty at the end of the day

Well honestly my dealer does. I go there every week for live food so see it often. Someone asked about cycling a tank as she'd read about it online but he said "not necessary, add water conditioner to get rid of chlorine and you're fine" I didn't say anything as he's a mate and didn't want to fall out with him.
Kelly if you re-read my post you'll see that all I said was how I do it. I never said not to cycle or test. It's fine if he/she wants to do it. If I were setting up a new tank I'd get the tank delivered today, set it up and add fish maybe tomorrow but only 3 or 4 hardy fish, regardless of tank size. I know a woman who put 40 fish in a new tank. Don't think I need tell you the outcome! If I had many fish losses then I would test maybe but so far must have been lucky then.

yes i agree, setting up a tank first then adding a couple of fish to kick start the cycle and still have something to look at is fine, and is also the way i do it, well now i just use gravel from my big tank which is well established. as long as the water changes are strictly carried out as and when needed.

what i dont agree with is the whole cycle is not needed thing, every aquarium cycles, well unless chlorinated water is added which will kill it off and put it back to square one.

in my opinion, i myself would never purchase any fish from a store which is happy to sell an entire set-up and the new fish all at the same time, also, if i had a friend in the trade who was doing so, i would encourage them to research what they are putting these poor fish through by doing so. the stress of moving to a new tank is in itself hard on the fish, but to be allowed to sit for what could be several hours while a new owner sets up a new tank, in a small plastic bag, in my eyes is plain cruel.

its just that people should be aware they need to do very regular partial water changes when its started and for first month or so until the nitrates take over and break down the often fatal ammonia and nitrites. hence the need to know about cycling, as long as they know the basics as to what and why, i dont see as there is a problem with fish in cycling, as long as the water is changed before it gets to the point of harming the fish, which with heavy stocking could be as much as every day. the only real way to keep check before losing fish is to test. i no longer test my water, i just keep on top of the changes.

the OP needed to know why his fish were dying, or still are dying, so in reality to try to find out we need to know exact water results just to cut out water quality issues, and has now asked what water parameters are acceptable, so if they are looking for acceptable numbers, then its 0 ammonia, 0 nitrites, and <40 ppm for nitrates. ph is fine pretty much no matter what as its best for fish to stick with a stable ph which is slightly out of what their ideal is than to have it waver and possibly kill them via ph shock.

not trying to argue, just im very fond of fish and they are probably the most neglected pet people own. the more of us that let people know the rights and wrongs of fish keeping, the better these little aquatic critters lives can be. we all try to do the best for our pets, fish should be no different

anyway, im off on holiday for a week and a half, so il not be on again for some time, i hope the OP manages to get his tank under control and starts to enjoy his fish and not have them turn belly up on him, good luck