Neglected Clown Loach

[LockdownLoach]

Hello everyone, thank you for having me here, very new to fish keeping and had to learn a lot in the past 3 months.

Ok so before I begin with the back story here are the basics:

* Type of fish that are affected? Chromobotia macracanthus (Clown Loach)
* How long has the tank been set up for? Technically 10+ years, however was moved 4 months ago. approx 50% water saved during transport.
* Size of tank (dimensions and volume): Not my tank originally but I believe it to be a Fluval Roma 125, Height 50cm, Width 80cm, Depth 35cm, Volume 125 Litres (27.5 Gallons)
* How is the tank being filtered? Fluval U4 with poly-carbon inserts and clear max inserts.
* Water temperature: 25 Degrees Centigrade
* Your maintenance regime: Weekly 20% water change, with gravel vacuum. Filter media had 50% change 3 months ago, along with filter sponge change and addition of clear max and carbon filters. Plan on changing the other 50% of media in a few months. Filter Sponge rinsed in bucket every month.
* Has anything new been added to the tank recently? 1 x Corydoras sterbai, 1 x Corydoras aeneus, 3 x Pangio kuhlii. 2 x Drift wood, There were some plants added, however these have been migrated to a larger tank that is cycling ready for them all to move. (All added 3 months ago)
* What other fish are in the tank? The Loach came with 1 x Panaque maccus (Clown Pleco)
* As detailed a description as possible of the symptoms the fish are exhibiting: The clown loach seems to have black patches on either side of it. Pictures attached.
* How long ago the affected fish were added to the tank, and how long the fish have been displaying symptoms: 10 years I believe. Black patches have appeared over past month.
* Your current water parameters - ammonia, nitrite, nitrate, pH : 0 Ammonia, 0 Nitrite, 40 ppm Nitrate, 7.4 ph.

Last thing before I begin, this was not my tank for a long time, it was a tank my work had purchased 10+ years ago. I did not choose the fish nor have any involvement with the tank until 4 months ago. The welfare issues with regards to tank size for fish, water conditions, and school size are all things I am trying to rectify for the benefit of the fish.

Background

I started at my work 2 years ago and for the entire time I have worked there has been this fish tank. Generally, it has not been kept in great condition. The algae growth and lack of maintenance often led it to being quite slimy. After the issue of the tank conditions was raised, they did pay for a local company to come in on a regular basis to perform maintenance on the tank.

At this point in time, there were, 3 Clown Loaches and 2 Clown Pleco (not certain, could have been 1 only).

Then with the Covid pandemic everyone stopped going into the office. I Like many others forgot about the fish tank (at this point I had never had fish nor researched it). There was one employee who went in regularly to feed the fish, however they were primarily given holiday food. This lasted for 8 months.. In that time, no maintenance was done on the tank whatsoever, bar giving the fish food.

In December last year I made a trip into the office for the first time since Lockdown here in the UK. When i saw the tank I was disgusted. The entire tank was black on all sides. You could not see into the tank. The water was clear enough to see through but definitely a disgusting brown colour. The lights, filter and thermometer were still running. In the time frame of those 8 months 2 of the Clown loaches had died (again, no water changed happened in this time). So there was one Clown loach on its own with a clown pleco. I went home that evening and spoke to my SO about the tank and how appalled I was, and that evening I made arrangements with my boss to move the tank to my care, and transport it to my house so that it could be looked after properly.

We got some brief advice from the LFS and picked up the tank that weekend. We managed to salvage about 50% of the water and transport the fish safely to our house. We gave the tank and initial clean to get rid of the majority of the filth, and get it on the road to recovery.

Bare in mind, this fish is meant to be 10 years old, yet it is tiny!

Here is a video of the state of the tank AFTER we did an initial clean of it, and first released the loach back into the water.

https://youtu.be/fz_zr9wHOSo

Here is the Tank 6 days later, after more dirt removal and fresh water.

https://drive.google.com/file/d/1DJliao ... sp=sharing

Then the addition of some plants to help eat up some of the nitrates.

https://youtu.be/B81dQrOm5VE

Lastly this is the tank 1 month after looking after it once I managed to get it stable (it was/is still a work in progress).

https://drive.google.com/file/d/1mhvs_n ... sp=sharing

So I thought all was going great, however I have noticed dark patches along the sides of the clown loach, you can see them in this video (note there were 2 filters in the tank at this point, this has now been reduce back down tot he single fluval U4) and in the photos.

https://youtu.be/-tWA6PyUsg0

https://drive.google.com/file/d/1l4dVL4 ... sp=sharing

https://drive.google.com/file/d/1zLYyWb ... sp=sharing

I am worried it is sick in some way, does anybody recognise it as an illness? can it be treated? or is it purely a stress thing from being in a small tank without any friends?

Lastly, my plans for the future (hopefully) with this fish are:

1. I have a much larger 300l tank for it to go into. This is currently cycling, but should offer a large improvement over his current tank. It has plants, sand, and wood.
2. I would like to get more Clown Loach for this fish to have others to school with, however my concern is that I do not have room for a tank larger than 300l currently.

Any other advice would be greatly appreciated!

If i have missed any details please let me know and i will try to edit this post for others to see.