We have added fish to our newly set up aquarium twice now and both times the fish were dead or dying within 24 hours. The pH is at the proper level. The tank was filled with spring water. Why do our fish keep dying?

It is possible the tank has not cycled properly which results in high ammonia and nitrite levels which can kill fish. Allow the tank to run, without fish, for at least 4-6 weeks. During this time, use a home test kit or submit a water sample for testing every few days. The local Petco may do this for free or for a small fee. What you are looking for is to have ammonia and nitrites at 0 ppm and nitrates at 20ppm or less. pH can hover around 7 for most community fish. Avoid large, rapid swings in pH though. What is happening in the tank during this time is that beneficial bacteria are populating the gravel/substrate and the filter. These bacterial populations are responsible for the Nitrogen Cycle. This cycle breaks down wastes from fish, uneaten food and plant matter into by-products that are filtered out or dissipate. You can "cycle" a tank with fish, however this increases the risk of loss. Once your tank has cycled, you can add fish. You will still need to monitor water chemistry and perform partial water changes regularly. Use only conditioned water that is temperature matched to prevent stress or shock. You will also need to vacuum the gravel regularly and rinse the filter media. Never use tap water to rinse. Use a bit of tank water to protect bacterial populations in the sponge.

The quick start liquid will add nitrifying bacteria but will not eliminate ammonia or nitrites. Both are harmful and can kill fish in high enough concentrations. You can use a home test kit to test the water or you can submit a sample for testing. Most pet stores or aquarists will do this for free or for a nominal fee. There are chemical additives you can use to decrease levels. When adding water, use treated water or aged water. Ideally, the tank should be left empty for about 4 weeks to properly establish the nitrogen cycle before adding fish. At this point, you may lose the second fish regardless of treatment. Test the water, make adjustments, let the tank cycle and start fresh. Adding an airstone can increase oxygen levels.

Cleaning the filter and changing the water may have upset the nitrogen cycle in your tank. This is due to removal of beneficial bacteria which convert ammonia (from waste, food, urine, etc.) to nitrites. Water and filter changes can be stressful as well. If you have the means, test your tank water for ammonia, nitrite, nitrate and pH levels. Adjust accordingly using conditioned water or additives that will bind harmful compounds. You can also submit a water sample for testing. Moat pet stores or professional aquarists will do this for free or for a nominal fee.

If persistent this is a very concerning but generic sign, which requires a logic but quite radical approach. Begin by submitting a water sample for quality testing. Most pet stores will do this for free or a nominal fee. High ammonia levels, PH imbalances may be responsible for that. Oxygen concentration and quality of the filters should be determined as well. If water quality is good and there are no major imbalances, your fish should get examined to look for any sign of bacterial/fungal infection and eventually water should be treated. Hope this answer was helpful, but please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.