I don’t understand what’s going wrong here…
I agree. I would not use any buffers, PH additives or other chemicals to solve any of this. The haze you noticed is likely ammonia levels rising in the tank. The problem you are having sound like they are caused by not having cycled the tank. Cycling requires some kind of waste (fish or food for example) in order to take place.
Here’s what I’d do: - Return all fish if possible except for one. - Monitor ammonia and nitrite daily and perform water changes as needed to keep the fish in health (use tap water not distilled). Also make sure you use a good water conditioner that removes chlorine, chloramine and heavy metals (Tetra AquaSafe for example). - 3-4 weeks later you should have both ammonia and nitrite levels down to 0 and nitrates starting to rise. You can now start to add a couple fish a week.
If you can’t return the fish, you will need to perform more frequent water changes in order to keep up with the rising ammonia or nitrite levels. Should you end up without fish, simply add a pinch of flake food each day to the tank to simulate the presence of fish and complete the cycling process wihtout any fish being harmed.
Obviously don’t touch the filter media if possible. As needed, rinse half the media in old tank water leaving the other half untouched for at least a week.
If you have any friends with established tanks (healthy ones), you can ask them to squeeze some “yuk” from their filter media into a container with tank water in it and pour it into your filter. This will introduce bacteria to the tank a lot quicker. Most bacteria starters you buy are somewhat questionable in their efficiency, Bio- Spira seems to be the one that stands out from the crowd if you can find it.
Patience is the most important ‘chemical’ you’ll need during this stage 
Some links of interest: http://faq.thekrib.com/begin-cycling.html http://www.gpodio.com/food_cycling.asp
Hope that helps Giancarlo Podio, LMD
Category: Philippines Internet Koi Society
