2. I feed him mostly pellets, whilst feeding him bloodworms, daphnia, and mysis worms once or twice a week for a varied diet.
You could drop the dry food and try feeding him frozen and live foods for a week and see if it helps. He can have frozen or live foods every day and it's not an issue. Just keep his diet varied.
I used to feed my fish dry food in the morning before work and frozen and live foods at night.
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3. I have never seen his stools, to be quite honest.
Monitor him and try to see what his poop looks like. It should be a solid colour (black, brown, red, etc). The colour will vary depending on what he eats.
If the poop is white and stringy, he has an intestinal problem.
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6. So far, once a month. Whatever cycle I did seems to be working very well.
7. I try to, but I don't think I have an effective way of getting all of the dirt out from under.
8. I do dechlorinate the water after every change.
You want to do partial water changes regularly to reduce the build up of nutrients, chemicals from the fish, and disease organisms that grow in the water. I like to do a 75% water change and gravel clean every week but a 50-75% water change should be done at least once every 2 weeks.
You should try to gravel clean the substrate every time you do a water change. You can buy basic model "gravel cleaners" from any pet shop and they come in a variety of sizes. You can also make them from a garden hose and 1, 1.5 or 2 litre plastic drink bottle. However, a 2 litre is probably too big for your tank.
To make a gravel cleaner, cut the bottom off a plastic drink bottle. Remove the lid and plastic ring too. throw these 3 bits in the recycling bin. Stick a length of garden hose or plastic hose in the top of the bottle and you have a gravel cleaner. You can look on YouTube for videos on how to use a gravel cleaner.
The following link has a picture of a basic model gravel cleaner about half way down the page.
https://www.about-goldfish.com/aquarium-cleaning.html
You need to dechlorinate any new water before it's added to the tank. If you get a couple of new buckets and use a permanent marker to write "FISH ONLY" on the buckets, you can use them for the fish tank and nothing else. Then add some dechlorinator to the bucket and fill it with tap water. Aerate the water and dechlorinator for at least 5 (preferably 30) minutes before adding it to the tank. The aeration helps mix the dechlorinator with the water and allows it to come into contact with all the chlorine/ chloramine molecules in the water. Aeration also helps get the dissolved gasses (oxygen, carbon dioxide & nitrogen) back to normal levels in the water. These gasses are sometimes forced out when the water is under pressure so aerating can help get them back to normal. You can have one bucket of water aerating/ mixing while the other bucket is used to drain dirty tank water into. The dirty water should be poured on the lawn/ garden outside.
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9.I have a QuietFlow 10 (not that quiet though). I haven't "cleaned" it persay, unless brushing the algae off counts.
Filters should be cleaned at least once a month. However, if the filter is less than 6 weeks old, do not clean it. Wait until it is 6-8 weeks old before doing the first clean.
To clean a power filter, simply wash/ squeeze out the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn.
The Quiet Flow filters have filter pads/ cartridges in them. The manufacturer usually recommends replacing these filter pads every month. Do not do that. It is a gimmick designed to make you give them your money. The filter pads develop colonies of beneficial bacteria that live on and in the filter media. These good bacteria help keep the water clean and free of ammonia and nitrite. If you replace the filter pads, you get rid of the good bacteria, and can have ammonia and nitrite problems in the water.
You can replace the filter pads with sponge and sponges last for years and get cleaned by squeezing out in a bucket of tank water. I used AquaClear sponges but there are other brands. Just find a sponge for a different brand of filter and use a pair of scissors to cut the sponge to fit in your filter. Have the sponge in with the old filter media for at least 1 (preferably 2) months, and then throw the old filter pad away. Add some more sponge and wait another month or two and then remove any remaining filter pads/ cartridges and replace them with more sponge.
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You might have Ammogon/ Zeolite in the filter pad. This is a white granule used to remove ammonia from the water. Zeolite will stop the beneficial filter bacteria growing for a while because it removes the ammonia, which is the initial food source for the filter bacteria. Eventually the Zeolite fills up and can't adsorb anymore ammonia, then you get an ammonia reading and the fish can get sick or die. This is one of the reasons why the manufacturers like you to buy replacement filter pads each month. So the Zeolite is replaced and can continue to remove ammonia. The problem is unless you test the water regularly, you never know when the Zeolite is full and needs replacing. So it's best to remove it to begin with and let the filter bacteria grow so you never have an ammonia or nitrite problem. And you save some money too.
You can check the filter pads/ cartridges for Zeolite by cutting a slit in one end of the filter pad and looking inside. If it has white or black granules in the pad, tip it out and throw the granules away. Then rinse the pad in a bucket of tank water and re-use the pad.
Carbon is a black granulated substance that is also put into filter pads. Again it isn't necessary and can be removed.
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WHAT TO DO NOW?
I would start off by doing a 25-30% water change and gravel cleaning the substrate every day for a week. Then increase it to 50% every day for a week. After that do a 50-75% water change and gravel clean once a week or once a fortnight (once every 2 weeks).
If there is a water quality issue or a build up of disease organisms in the water, the daily water changes will help by reducing any issues in the water.
Start off with small water changes because it is less stressful to the fish and will reduce the variation between the tap water and the aquarium water, which might be significantly different due to not being changed regularly. Gradually build up the size of the water changes.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Give the filter a clean but don't replace any filter media/ materials.
Get some pictures and video of the fish and tank asap.
Monitor his poop.
What sort of gravel is on the bottom of the tank?
Some fish are stupid and eat gravel and it doesn't get pooped out. Then they sink to the bottom. Monitor the fish and make sure it isn't eating the substrate.
