1. How many PPM of Nitrate is safe in aquarium?
On the safe side, get it as low as possible.. Best is below 10ppm.. 25-50ppm is still acceptable..
2. Read a post that if all NH4, NO2 and NO3 are zeros during new tank cycling, it could be that the tank never went through ANN cycle. Is it true?
I am not sure about this.. By right, for the ANN cycle to be fully completed, NH4, N02 will reach its peak and drop to zero respectivily. Den N03 will rise to its peak and by den you will need to do a 25% water change.. To reduce the Nitrate level..
3. Since Nitrate is the final product of ANN cycle, will it finally reduce to zero? Today is the 18th day of my new tank cycling, the NH4 is 0 (first measure was 1PPM), NO2 is 0.1PPM (it was around 0.3~0.8PPM) and NO3 is around 5~10PPM (it was around 20PPM). Can I say that my tank has completed the cycling and it is ready for LS?
If my memory served me right, Nitrogen gas is the final end product.. When the anaerobic bacteria break down the Nitrate.. This is done in the DSB where all the anaerobic bacteria reside..
4. The filter wool is very dirty. Should I just replace it or clean it? I heard that it might contain beneficial bacteria? Is it true?
Yes, it contain bacteria but also will be a nitrate factory.. Best to change every week to prevent your nitrate from rising..
5. I have just measured my tap water using API NO3 test kit, the reading was 0. Read from forum that it is better to treat the tap water with Crstal Pro before pump it into the fish tank. Anyone has experience with this product? 3 stage or just single stage is good enough?
Yes, our tapwater contain chlorine, heavy metal and other chemical.. So it is better to go thru RO or DI filter..
6. What could be the source for the high NO3 in the fish tank? My existing 1 1/2 ft tank read >40PPM. How can I reduce it? Do a water change?
Can do the water change.. And Nitrate reducing product like AZ-N03..
Please help.....