How can I improve my freshwater aquarium's water quality?

Question

I re-set up my aquarium about a month ago, and I had several guppies and a pleco. Now, all the guppies have died and only the pleco has survived. I recently added a betta also. I took some measurements of the water quality and the readings came out like this: nitrates: 40 mg/L, nitrites: off the charts (much more than 10 mg/L), soft water ( approx. 75 ppm), between 120 and 300 ppm alkalinity, and a pH of about 8.4. What can I do to improve the water quality and not kill anymore fish? The tank possibly hasn't cycled yet.

Answer 1

You're right about the cycle.  What happened is when you set up your aquarium, there was no beneficial bacteria to break down those nitrites.  These toxins are most likely what killed your guppies, I'm surprised the pleco is still alive.  You need to do water changes pretty often right now.  At least 10% a week.  If you know someone with an established aquarium, you can get gravel or filter media which will have some bacteria on it to help you boost your own culture of bacteria.

Live plants can help a little with breaking down nitrogenous elements in the water.  Be careful not to overfeed as well, this caontibutes greatly to the buildup of toxins.

Answer 2

your tank probably has not cycled yet so just be patient and don't buy any more fish for a few weeks

Answer 3

add some cycle(the product) right now to whomp up your nitrite eating bacteria.

nitrites and pH are the culprits. pH can be fixed by water changes or a product called pH down. do pH changes gradually.

the pleco might survive, but don't count on the betta.

Answer 4

Pull your tank down again. Wash everything in it, replace it with bottled water and replace you biologic filter pack. Monitor everyday for a week and chart the nitrates. Do Not use tap water ever. Nitrates should show a rise and then level off.