Silver dollar with white discoloration on face and head

[Penelope .R]

Hi again. I will start by saying that I wish others will offer their opinions about what is going on with your aquarium and your fish. I don't want to be 'the (only) monster with the bad news', and I can be wrong as well. I encourage other forum members to chime in to try to help you in this situation.
I will say this-
Nitrate - In an established aquarium such as yours (with a decent bioload including largish fish, sparsely planted, potentially having a routine of less than enough water changes), the probability that nitrate is at zero on average is very low and would be hard to explain or imagine. If indeed you have tested, I suggest the test kit is giving you inaccurate results, either because the solution (drops) is spoiled, the directions for the assay are not followed correctly, or something else is affecting the assay; if test strips (not drops) are being used, then they may be too old and not responding. A new kit may be in order. In the meantime, you can always bring a sample to your near pet store and they will test the water for you. However, having a working test kit, particularly if having fish health issues, is absolutely necessary. And nitrate levels (average, not so much just after a water change) are the most informative in your situation.
Fish health (silver dollars) - The one silver dollar that started this thread, IMHO, is past the point of no return. The circumstances that resulted in his current condition did not occur quickly or in a short period of time. Instead, he has been declining for possible months or more. It is very likely that internal parasites played a role, as well as other circumstances (bottom of the pecking order, poor water quality, etc. I cannot not know, I am just listing various possible reasons). I strongly believe it is a combination of factors. If parasites played a role, the agent is in the tank, whether all fish show acute symptoms or not. It is not unusual for some fish not show ill effects even in the presence of parasites; however if some fish have a weakened immune system (for whatever reason), that fish will fall ill before others. But all are exposed to infection.
The other 3 fish are two males and one female. I made clips of some of your photos to point out the items I refer to below. Please don't be offended but you need to know these things.
All are quite skinny but that is solvable.
All of them have the outer edges of most fins frayed and with visible light fungal/bacterial? (not sure) infections. The frayed edges may have started with the rossy barbs nipping at them (not sure, but you may have observed it?), upon which secondary infections have set in. Again these things are solvable but if not addressed they become serious.
One of the males has its right eye swollen (exophthalmy). Typically this results from a bacterial infection. If not addressed, this can become very serious and result on loss of an eye, or impaired vision and more. The same fish has a white infective body on the lower right side, just above the anal fin (photo 2. Not the dots in photo 1, which I think is an artifact). Not sure what that is about. Although average quality photos are sometimes misleading, and there is a lot 'grain' in the photos, as well as particles floating in the water, I believe the items I pointed out are real, because they show in more than one picture, in the same fish and position. You would be the better judge of that.

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The other fish (barbs, danios, cardinals) - You are right in that they look Ok to me. The one barb that looked off before, may just be due to a bad picture/angle. Again, sometimes some fish are better at fending off conditions than others.
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One other note. If I understood correctly, your only filter is the Hydor canister (fine filter, BTW). I would suggest 2 things towards improving water quality. These may or not work for you, but it is what I use and I think they make a huge difference:
i) I would use a prefilter on the intake, to impede solids and food to go into the canister. I clean the prefilters of all filters weekly, and the media in HOB filters weekly as well. The media in canisters less frequently. Since your filter is serviced monthly, without a prefilter there is too much time for maladies to get inside and to fester in there.
ii) I turn the filter off in my tanks during feeding (I have them all on on/off switches). Again, it maintains filter media much cleaner.

Foods (I use this for all my fish, larger size particles for silver dollars) - My fish are mainly south american omnivorous characins and cories, but also others such as gourami, rainbows, plecos) -
I don't know anybody who feeds like I do, and I don't expect anybody to do as I do. However, since you ask, here it goes. I believe in variety, and I don't believe in strict carnivores, nor strict vegetarians.
Unless I am raising fry, adult fish get fed only 4 days per week. However, all my tanks are planted. On the no-food days, I do hang pieces of nori (seaweed) from clips, who are loved by all (photo).
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On feeding days, fish 2 different items out of a long list of rotating items, including: Flakes (3 kinds), pellets (12 kinds), frozen (4-5 kinds), Repashy (2 kinds), earthworms (I keep a culture), dry meal worms, garbanzos. For silver dollars, in addition to above, I include sunflower seeds in the rotation. Sometimes I use cucumber (rarely). For commercial brands, I keep NLS (small pellets), KensFish (pellets, flakes & discs), Repashy, and Hikari (frozen). I also make a mix of several varied flakes, pellets & discs (ground with a dedicated coffee mill) that allows feeding large size food to small fish. I keep the stock of each kind frozen, and smaller amounts ('my stash', photo), in a refrigerator, for regular use.
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Using this feeding regime accomplishes two things: Everybody gets a varied diet (I can make it heavy on one or another item for individual tanks or fish), AND, nobody develops 'habits' where they would only accept this food or that. Not on my watch.

Ok, I hope this helps (that was my lunch break). I hope others chime in with their input on fish health.
Good luck!

Thank you so much for your response. I'm glad the Rosy barbs are okay at least and you don't need to worry about being the "only monster" to give me bad news, I appreciate your honesty. I do think I misunderstood parts of your previous posts and that you possibly misunderstood parts of mine, but that's neither of our faults

I actually got the water tested at my local fish store two days ago to check the accuracy of my kit, nitrates at 0 at the time. Like I said I just cleaned the filter and have been doing daily changes before this so it may have been higher before, I'm not sure and there's no way to know now. I also double checked with my kit, it's an API master test kit (I think thats what it is called). Nitrates still at 0. I can't explain it as you said, other than because of the daily water changes for the last 2ish weeks.
From here out I'll aim for larger water changes 2-3 times a week to increase water quality, I thought 50% once a week was okay before but I'll adjust the schedule.

Now for the other silver dollars-
I had no idea they were skinny, they've always looked the same. Can this be fixed by feeding a more varied diet or is this more a sign of parasites?

As for the frayed fins, the one with what you said is a swollen eye has frayed fins, I believe it is injurys he sustained in a water change, although I could be wrong, as I only noticed it a few days ago. I've never seen the Rosy barbs pick at the dollars but it'sof course possible I've just been missing it. I don't think the patch by the anal fin of the same fish is anything concerning, he's had a mark there for years, like his sales reflect the light differently.

How can you tell his eye is swollen also? I am curious as that fishes eye has looked like that since I started taking care of him 4 years ago and hasn't changed. I assumed the difference of that eye was an old injury or an effect of a sickness that happened before that I don't know about. I'm googling it now.

The other two fishes fins aren't frayed, I believe the pictures are showing the little bubbles and particles that collected on their tails and fins after that days water change, they are completely gone now.

I've used pre filters before, they always seem to get clogged despite weekly cleanings and slow down the filters output, even when I feed very little.
Turning off the filter during feeding is a fantastic idea though and something I will implement.
I am saving to get a second canister filter to install at the other side of the tank as well, but I can’t afford it yet.

Thank you for describing your feeding regimen. I was at the fish store yesterday looking at what frozen foods they have available and I've been researching commercial foods I can rotate between.

Is there something else I should be doing now other than water changes? Medications or treatments I should get? I am researching internal parasites in the meantime.

And again I appreciate it, and I appreciate your honesty. I am always learning more and I admit fish were never something I wanted or knew much about, it's hard to explain but this tank literally just fell into my lap, I'm just doing the best I can for the fish I have now, even though now it seems like I've been failing the whole time. Anyway, truly I appreciate your help and knowledge, you've given me a lot to improve upon.