Large water changes that include more than 60% water change, rinsing gravel, cleaning filter media lead to a complete, massive change in the water chemistry. Fishes when put in these new conditions, lead to temperature shock, stress, loss of appetite, and then death.
Because the fish live in the water and the changes happen gradually, they adjust to it. When a sudden, large water change occurs, it causes such a drastic shift in the water parameters that the fish often cannot tolerate it and they die.
I do a partial water change in order to maintain uniform water parameters like ph, gh, salinity, hardness, & temperature. If you are doing a 100% water change chances are all these parameters will greatly disturb. This will in turn shock the fish body system and will perish within few hours.
Larger water changes seem like they would be better, however, you can bring on a lot of stress to fish and plants with drastic water changes. The goal of changing water is to keep the fish healthy. If doing a large water change causes stress and illness, then it's not completing our goal.
In some cases, mild stress is something your aquarium fish can recover from but, in many cases, it is an early sign of something that can become a major problem. To maintain the health of your aquarium fish, you need to learn how to identify the signs of distress.
Municipal/Tap Water
Most municipalities treat drinking water with either chlorine or chloramine for disinfection purposes. Chlorine is extremely toxic to fish and needs to be completely removed before the water comes in contact with fish. Chloramine is chlorine bonded to ammonia, both of which are detrimental to fish.
If you dechlorinate properly and always bring water to the same temperature, there is actually no limit on how often you can change the water. Professional fish breeders may change water daily in order to remove excess food and encourage maximum growth.
On the other hand, if your tank's pH is (for example) 6.3, while your replacement water has a pH of 7.5, replacing 50% of the water all at once will change the pH of your tank significantly (possibly more than 50% depending on buffering factors), which will stress your fish, possibly enough to kill them.
The most efficient way to rid your aquarium of pollution from a dead fish is by exchanging some of its water. You won't need to clean the entire tank, but removing any contaminants that could have leached into the water is critical. To determine how much water to replace, You can use the test kit results.
There are many reasons why fish in your tank keep dying. A few reasons include stress, incorrect tank setup, overfeeding, diseases, and much more. To a beginner, it could look like your fish died for no reason whatsoever.
Even though you replace the old water with the fresh and purest one, the fish may not attune to this newness and drastic changes in pH, hardness and other water parameters. Some fish may die immediately, and some may fall sick, leading to their death over a week or so.
The two biggest reasons for fish illness are stress and dirty water. While some healthy fish can fight off the infection and get healthy, the weak ones may die. Therefore, it is important to watch for the signs of stress in your fish. Ich– It is a parasitic infection that passes in one fish from another fish.
Check the fish's eyes.
Look at the eye as a whole. If they're sunken, your fish is dead or near death. Look for cloudy pupils, which is also a sign of death in most aquarium fish. If your fish is a pufferfish, walleye, rabbit fish, or scorpionfish, occasional eye cloudiness might actually be normal.
If you are sure your tap water contains chlorine and not chloramine, you can let the water sit for 1-5 days to allow all the chlorine to evaporate. To speed up the evaporation process, aerate the water with an air stone for 12-24 hours or boil the water for 15-20 minutes.
Does Boiling Water Remove Chlorine? Yes, boiling water for 15 minutes is one way to release all the chlorine from tap water. At room temperature, chlorine gas weighs less than air and will naturally evaporate off without boiling. Heating up water to a boil will speed up the chlorine removal process.
Generally speaking, most species of freshwater fish won't live long if the tap water isn't treated. Untreated tap water can quickly kill fish in just a matter of hours.
To deal with dying fish even when the water tests perfectly, you can try stabilizing the water temperature, creating a schedule for feeding, finding the correct mates, and upgrading to the right tank size for your fish. It's also essential to move the aquarium to a safe location.
If the fish keep dying, but the water is fine, this points to illnesses, old age, poor feeding habits, poor tank conditions, toxins from external sources, and prior problems with the fish.
Freshwater fish have to invest a lot of energy keeping their internal fluid salt concentration from being diluted by the influx of water across the gills. Increasing salt levels in the aquarium reduces the water influx and releases energy which can be used dealing with stress and fighting disease.
Constipation, enlarged organs, or infection can all cause the swim bladder to stop functioning properly. Swim bladder disorder refers to issues affecting the swim bladder, rather than a single disease. Affected fish will inappropriately float or sink.
If your fish is swimming frantically without going anywhere, crashing at the bottom of his tank, rubbing himself on gravel or rocks, or locking his fins at his side, he may be experiencing significant stress. Talk to your veterinarian about treatment and look into what may be causing the stress and alleviating it.