# Dark spot on fish



## masa (Jan 20, 2021)

Hey!
I have 2 Corydoras living with my turtle in a tank, and today I noticed my albino corydora has a dark spot in the belly. I did a little research and it could be either the dark/black spot disease or pregnancy. Could you tell me what is it? 
Also, I don't know how to identify their gender :/
Thanks for the help!!

Masa 

P.S.: the other corydora is bigger and I also uploaded a photo so you can see what it looks like?? Anyways, thanks


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## LinznMilly (Jun 24, 2011)

masa said:


> Hey!
> I have 2 Corydoras living with my turtle in a tank, and today I noticed my albino corydora has a dark spot in the belly. I did a little research and it could be either the dark/black spot disease or pregnancy. Could you tell me what is it?
> Also, I don't know how to identify their gender :/
> Thanks for the help!!
> ...


Hi. Welcome to the forum.

Do you have any test results for ammonia, nitrite, nitrate and pH? Plus the type of test kit you're using.
How big is the tank?
Could you post a pic of the tank? 
How long have you had the fish?

Cories are egg layers, so it won't be "pregnant".

Do you only have the two Cories? Because they're shoaling fish and require at least groups of 6, preferably 10+.


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## masa (Jan 20, 2021)

Hi!!!
Thank you so much for the reply! Today I did some tests (the test kit is from Sera) and here are the results:
pH - 6.4/6.8
kH - 3°d/6°d
gH - >6°d
NO3 - 10 mg/l
NO2 - 1 mg/l
Cl2 - 0.8 mg/l
The tank is the Tortum 75 (75x36x25cm).
I only have 2 cories, but I'll get more when I get the chance to. I have had my fish since 13th of February.
I have attached a photo of what the results should be according to Sera and a photo of the tank just like you asked.
Hope it might help.
Thanks again for sharing your info and helping me.

Masa 

P.S.: I know the aquarium looks very poor but I haven't had the money to invest in some decorations. If there's anything that is absolutely necessary, please tell me. Also, the water level is low because of the Basking spot. But, eventually in the future, I'll try to create a basking spot over the aquarium so I can rise the water level.


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## NaomiM (Sep 22, 2012)

Hi,

You need to get your ammonia and nitrite levels down. It's possible the dark patch is caused by ammonia burn. Did you cycle the tank before stocking it? If not, your filter is now going through a cycle - in other words, it's trying to build up enough good bacteria to process the ammonia from the fish/turtle's waste into nitrite, then another batch of bacteria to process the nitrite into nitrate, which is less harmful and can be removed b regular water changes. Google the nitrogen cycle for more info.

In the meantime, I suggest changing 50% of the water daily and adding a product called Seachem Prime, which replaces your usual dechlorinator but also detoxifies ammonia and nitrite. It seems quite expensive initially but a little goes a long way, so it ends up more economical than most dechlorinators, too. Each day when you do a water change, add a dose that's sufficient for the whole volume of water in the tank. Repeat daily until ammonia and nitrite are <0.1.

In terms of additions to the tank, the corys would greatly benefit by giving them some sand to root through, as this is their natural behaviour. If funds are tight, cheap Argos play sand is fine, or any play sand that doesn't have added dyes or fungicides or anything of the sort. Wash it thoroughly and I suggest using a plastic bottle to add it without it going everywhere and clogging your filter up - this video shows how: 




Other cheap additions that the fish would benefit from include caves made from empty coconut shells (clean them well and boil them first) and aquarium safe rocks such as granite and slate (test them first with a few drops of vinegar; if it fizzes, they're not safe). Clean and scrub them well, and you could pour boiling water on them to help sterilize them, but don't boil rocks as they may explode!

Fish need places in the tank to hide or they will be stressed. Also, I don't know much about turtles, but I imagine there's a risk it may try to eat them? If so, they'll definitely need some hiding places! (Corys have spines, so could be dangerous for the turtle too if it did catch them!)


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## masa (Jan 20, 2021)

Hi!!
Thank you so much NaomiM. I was searching for some ammonia tests and the prices are a tiny little bit high... I found another thing that I don't know if it could help: Sera Toxivec. Basically, eliminates ammonia and nitrites. It's a cheaper product and I wanted your opinion on it. Do you think, instead of doing the ammonia tests, I could just use this product and try to keep the ammonia and the nitrites at a low level?
I do almost daily water changes, like 15% each time, and on the weekends I do a 50% and 100% in the next one. It depends.
About the decoration, I will definitely try the idea of the coconut. The turtle has never been aggressive towards the cories so I don't think this was caused by him.
The mark has softened its intensity but it got a bit bigger.
Again, thank you so much for everything.

Masa


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## NaomiM (Sep 22, 2012)

masa said:


> Hi!!
> Thank you so much NaomiM. I was searching for some ammonia tests and the prices are a tiny little bit high... I found another thing that I don't know if it could help: Sera Toxivec. Basically, eliminates ammonia and nitrites. It's a cheaper product and I wanted your opinion on it. Do you think, instead of doing the ammonia tests, I could just use this product and try to keep the ammonia and the nitrites at a low level?
> I do almost daily water changes, like 15% each time, and on the weekends I do a 50% and 100% in the next one. It depends.
> About the decoration, I will definitely try the idea of the coconut. The turtle has never been aggressive towards the cories so I don't think this was caused by him.
> ...


I've not used Toxivec so can't comment on effectiveness, but Prime really is the best for overall economy as it's mega-concentrated and you only need tiny amounts, so one bottle lasts for months and months. Looking on Amazon, 100ml of Prime is only a couple of quid more than 50ml of Toxivec, and it will last much much longer. For best economy, also get a 1ml syringe for accurate dosing (£1 for 10 from ebay). But if you can't get Prime, it looks like Toxivec would do instead.

Your water test is showing high levels for Cl2 - are you currently using a dechlorinator? (I didn't look properly initially and thought this was the ammonia level, but then if you have nitrite present, this is proof that you've had ammonia recently even if you don't have it now.) If you're not currently using a dechlorinator, you need to get one urgently - either Prime or Toxivec will cover this as well as the ammonia and nitrite. Chlorine is not only harmful to fish but will also prevent the filter from developing the good bacteria necessary for long-term processing of the ammonia and nitrite.

In the long term, yes, you will need an ammonia test as it's the first thing to check if you have any problems, but if you can't afford it right now, just assume you do have ammonia and carry on with the Prime/Toxivec and water changes. You definitely have nitrite, and the advice for dealing with this is the same as for ammonia anyway.

Don't do 100% changes as it will seriously stress the fish. Better to do more frequent 50% changes. Once you've dealt with the ammonia and nitrite problems, you can go down to weekly 25% changes if you're not overstocked, but I have no clue about a turtle's bioload, so might be better to ask on the reptile forum about whether the water volume you have is sufficient there.


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## masa (Jan 20, 2021)

NaomiM said:


> I've not used Toxivec so can't comment on effectiveness, but Prime really is the best for overall economy as it's mega-concentrated and you only need tiny amounts, so one bottle lasts for months and months. Looking on Amazon, 100ml of Prime is only a couple of quid more than 50ml of Toxivec, and it will last much much longer. For best economy, also get a 1ml syringe for accurate dosing (£1 for 10 from ebay). But if you can't get Prime, it looks like Toxivec would do instead.
> 
> Your water test is showing high levels for Cl2 - are you currently using a dechlorinator? (I didn't look properly initially and thought this was the ammonia level, but then if you have nitrite present, this is proof that you've had ammonia recently even if you don't have it now.) If you're not currently using a dechlorinator, you need to get one urgently - either Prime or Toxivec will cover this as well as the ammonia and nitrite. Chlorine is not only harmful to fish but will also prevent the filter from developing the good bacteria necessary for long-term processing of the ammonia and nitrite.
> 
> ...


Hi NaomiM!!
Seriously, thank you so much for all the info. You are a true hero 
Unfortunately, Prime doesn't get sent to my address, so I guess Toxivec will have to do. However, I was looking for other water products and I came across Sera Aquatan. On their website it said that you could combine them (the aquatan and the toxivec), should I buy both or do I just buy the Toxivec?
The only product that I use in the water is the Turtle Clean from ExoTerra (+ calcium block in the water for the turtle).
The other Corydora seems completely fine, with no marks or spots.
I'll definitely buy the ammonia tests when I get the chance to.
Recently, I did notice some brown things in the aquarium, which I assume is Brown Algae. Do you think this might have anything to do with what's happening?
Thank you for all the recommendations and advice. It really helped me.

Masa


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## NaomiM (Sep 22, 2012)

Again I'm not familiar with Aquatan, but reading the specs on their website, it looks like Toxivec is the one you need. Aquatan mentions dealing with chlorine and ammonia, but doesn't mention nitrite, while Toxivec mentions all three. Also, Aquatan adds calcium, which as you already have a calcium block for the turtle, I think it's best not to overdo it by adding another calcium product, especially with the corys, as they prefer soft water without too much calcium.

Yes, the brown algae (also called diatoms) is very common in new setups. Basically the ammonia acts as a fertiliser for it. You can wipe it off with a sponge, or there's a type of snail called the nerite snail that is a very effective algae eater, but I don't know if your turtle would see that as a snack?


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