When is a 90% water change necessary and how to take care of it?
A 90% water change is necessary if the aquarium water is toxic for your fish and they are showing signs of poisoning! If your discus fish are “shooting” through the aquarium, it is very likely that this is a sign of poisoning. This can happen, for example, if you feed more than your filter can break down (nitrite poisoning).
If you have detected traces of nitrite, when testing your aquarium water chemistry, you should first cut the feeding amount and not cease feeding straight away. The behavior of your fish will tell you when the nitrite level is too high because they will refuse their feed and breathe heavily and quickly. Should you observe this behavior in your discus
fish, you must immediately stop feeding and carry out a 90% water change. Only once the nitrite content and/ or the ammonium content and/ or the ammonia content of your aquarium water has reached zero again, should you gradually begin to feed your fish again.
Use a bucket and hose to remove 90% of your aquarium water and Re-position your filters, so that they continue to filter the aquarium water for as long as possible while the water drains and so that they can resume the filtration of the water as quickly as possible, when you are re-filling the aquarium. When you re-fill the aquarium, you must use water of a suitable temperature (approx. 28°C / 82°F) so that your fish will not be swimming in cold water. Carefully pour the first buckets of fresh water slowly against the inside of your aquarium wall, as your fish are likely to be nervous due to the low water level and may startle and/ or injure themselves.
If your tap water is very soft (GH 0 – 5), you may need to do water changes more frequently. Also, if the pH value falls from say, 7.5 to 6.0 in a short period of time you should do a water change immediately. Otherwise the pH value – and hence the acidity of your aquarium water – will drop very quickly. If the pH value reaches 3.6, the acidity is so high that it is lethal for your fish. If the stocking density of your aquarium is low, you can reduce the volume of the water you exchange or how frequently you carry out a water change, as appropriate.