A small hole on the dorsal fin: is it ph related?

[lanpen]

Today I noticed a small hole on my betta's dorsal fin, as you can see below:










My setup is as follows:
• Tank size: 15.74" x 11.81" x 9.84", holding 7.29 gallons;
• Substrate: 11.02 lbs of Aqua Pedras gravel nº 0;
• Heating: Roxin HT-1300/Q3 50 W, set to 26 ºC;
• Filtration: Xynyou xy-2835 sponge filter with Tetra Whisper air pump;
• Lighting: 4.8 W, 12 volts, 7.87" LED;
• Photoperiod: 11 hours daily, with Coibeu YTS-823 timer;
• Inhabitants: Betta splendens;
• Plants: Elodea sp., Ceratophyllum demersum, Taxiphyllum barbieri, and Salvinia minima;
• Other organisms: Cyanobacteria and something else;
• pH: 7.5 or higher;
• Ammonia/nitrite: 0/0 ppm;
• Maintenance: 20% water change every two weeks;
• Feeding: Poytara Betta (Monday to Thursday), fasting on Friday, live Artemia franciscana on weekends.

I'm trying to lower the pH using almond and chestnut leaves, but no success so far. My tank has been cycled since last month.

Thanks for your attention.

Note:
[1] Poytara Betta food isn't well-known outside Brazil, but its main ingredients include fish meal (tuna and sardine), salmon meal, squid meal, brine shrimp meal, and flaxseed meal. It guarantees 35% crude protein, 6% crude fat, and 2.5% fiber.

[barnicle]

To help you figure out what's going on with your betta, it'd be great to know your water hardness. Betta generally do best in soft water. Considering the fin issue, I'd recommend doing bigger water changes more frequently - daily, in fact - rather than every two weeks. Fin rot often stems from poor water quality, and fresh, clean water is usually the most effective cure. Once your betta's fins have healed, you can scale back to a larger weekly water change.

You should also consider getting rid of that cyanobacteria; it's not doing your tank any favors. And I have to say, your betta is indeed lovely.

[lanpen]

I appreciate your input, barnicle. I'm considering your suggestions and I'd like some further clarification.

What percentage of water change would you recommend for daily changes? I'm concerned about shocking my betta with drastic changes, so I'd like to proceed cautiously.

Regarding the cyanobacteria, I'm open to advice on how to eliminate it. I've read about various methods, but I'd like to hear your thoughts on the most effective approach.

As for feeding, do you think I should make any adjustments to help my betta recover? Perhaps incorporating more live food, like the artemias, could be beneficial?

I'm also wondering if I should reevaluate the food directions for my betta food. I'm concerned that I might be overfeeding him, especially with the combination of betta food and artemias.

I plan to use the siphon to remove detritus, as I'm hesitant to disturb the substrate. Given that my ammonia and nitrite levels are zero, I'm assuming the poor water quality is likely due to an excess of organic matter.

[barnicle]

I'd say start by siphoning out the cyanobacteria with your daily water changes, don't worry if some sand gets taken out, you can always top it up later. Frequent and big water changes will really help dilute those excess nutrients that the cyano's feeding on, so give that a go and see how it goes.

[TankWarrior]

Honestly, I think you're overreacting. That hole is barely noticeable. If you're doing regular water changes, like every few days, your tank is probably fine and your fish is healthy. Its immune system is likely strong from all the good care. If that sounds like you, I wouldn't worry about it.

[lanpen]

I've come across a few instances where people successfully eradicated cyanobacteria using azithromycin. I'm not sure if it's worth trying, though - has anyone else had any luck with this method?

Recently, I added a curtain to the window on that side of the tank, hoping to reduce the amount of light that's contributing to the issue.

I did a partial water change today and removed some of the affected areas, which seems to have gotten rid of that awful smell - probably from the cyanobacteria.

[lanpen]

Today I recorded another video of my lovely betta's dorsal fin.

The water became less turbid after the partial water change, and this also improved the illumination - even with my simple desk lighting setup, using an old fluorescent lamp.

[barnicle]

I've never used chemicals to kill cyanobacteria, but @sSjey might be able to help you with that.

If you're not using a hose to change the water, I'd suggest you start doing so. That way, you can be more precise about siphoning out the cyanobacteria - it tends to come off in big sheets. To be honest, I think I would strip the tank and start again after giving it a good cleaning. You've got a few things working against you - low flow, a lot of detritus buildup, and not enough plants to use up the excess nutrients, plus a fairly bright light, which is basically a recipe for cyanobacteria growth.

One thing you could try is covering part of your light with black tape to dim it a bit, and reducing the lighting period to 8 hours. You need to do bigger water changes - at least 50% - to get rid of all the mess that's gathering on the substrate, and you need to do them more often than once every 2 weeks. Most people do water changes at least once a week to keep nitrates to a minimum. Adding more live plants will help to keep the cyanobacteria at bay, as they'll outcompete for the nutrients, but reducing the light is what's going to help the most.

[sSjey]

Honestly, I'm stumped when it comes to cyanobacteria. Never had to deal with it personally, so I'm not much help there.

[lanpen]

My sipLion looks like this:



I've been keeping fish since 2012, and this is my first encounter with cyanobacteria in any tank. I'm not sure I agree with stripping the tank and starting from scratch - it took over a month to cycle, and here in Brazil, there aren't any reliable biological accelerators available. When I had a phytoplankton bloom, many people suggested I do more frequent water changes, but I didn't want to risk crashing my biological filtration. Instead, I decided to wait it out, and the issue resolved itself after a few weeks. However, I'm aware that phytoplankton and cyanobacteria are different, and my main concern is the hole on my betta's dorsal fin.

Given that cyanobacteria are bacteria, antibiotics might be the only effective solution. But I'm worried that using antibiotics could harm my biological filtration. For now, I'm going to look into buying more aquarium plants to help combat the issue.