Filter Fluval external cannister. Polywool, Foam, Ammonia remover and Carbon replaced 3-4 weeks, Biological
material rinsed same time, Filter body and hoses cleaned at same time
If you have ammonia remover in the filter, it will stop the beneficial filter bacteria from developing properly and you can have ammonia spikes occurring between the times you change the ammonia remover.
You can recharge the ammonia remover by soaking it in salt water for 24-48 hours. But I would stop using it altogether.
You don't need carbon in the filter either. It is used to remove chemicals after treatment and will remove tannins (yellow staining from driftwood), but these can be removed with water changes.
Polywool can be replaced with sponge. If you want to keep using it, rinse it under tap water and re-use it. Replace it when it starts to fall apart.
Foam/ sponges don't need to be replaced unless they start to fall apart. Most sponges will last 10+ years. You clean sponges by squeezing them out in a bucket of aquarium water and re-using the sponge. The bucket of dirty water gets poured on the lawn.
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Gravel "vacuum" cleaned every 2 days, approx 20% water change at this point.
Bigger water changes are more effective when it comes to diluting nutrients and disease organisms in the water.
You do water changes for 2 main reasons.
1) to reduce nutrients like ammonia, nitrite & nitrate.
2) to dilute disease organisms in the water.
Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things that make your skin crawl. Doing a big water change and gravel cleaning the substrate on a regular basis will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish.
If you do a 25% water change, you leave behind 75% of the bad stuff in the water.
If you do a 50% water change, you leave behind 50% of the bad stuff in the water.
If you do a 75% water change, you leave behind 25% of the bad stuff in the water.
Fish live in their own waste. Their tank and filter is full of fish poop. The water they breath is filtered through fish poop. Cleaning filters, gravel and doing big regular water changes, removes a lot of this poop and harmful micro-organisms, and makes the environment cleaner and healthier for the fish.