Away for the weekend and 3 fish deaths?

[Kitkat127]

Tank size: 20 gallon long
pH: 7
ammonia: 0
nitrite: 0
nitrate: 20-40 ppm
kH:
gH:
tank temp: 78

Fish Symptoms (include full description including lesion, color, location, fish behavior): once getting home our big momma was basically laying at the surface not able to swim very well or stay at the bottom like bloat but she was not bloated just very pale and an extremely white stomach which when we left tank parameters were the same as when we got back. Our sterbi had passed away the day before no idea looks or condition before death. Then this morning our bristlenose pleco was found loading upright at the bottom of the tank appeared to look normal. I am so lossed and confused as to why my fish died.

Volume and Frequency of water changes: Weekly 5 gallon change

Chemical Additives or Media in your tank: 3 flourish tabs under sand pottassium by seachem every other day a capful, when doing weekly water changes add a capfull ph regulater by marineland, and 5 ml of tap water conditioner by API. Filter system aquaclear 50 with a sponge then another sponge then creamic rings all for biological filtration which are rotated on a weekly/monthly cleaning cycle.

Tank inhabitants: Down to two peppered corydoras one jullii corydora an albino corydora and 3 ghost shrimp. We have two cyrptocorynes in the tank which are ok not in the best of shape Brazilian water weed which is doing phenomenal and coontail which has to be trimmed a lot because of how well it's growing.

Recent additions to your tank (living or decoration):

Exposure to chemicals

 

[Colin_T]

It sounds like a bacterial infection. Do a 75% water change and gravel clean the substrate every day for a week. Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

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Aquatic plants don't really need much potassium. Terrestrial plants use it to produce fruit, seeds and help general health. Aquatic plants don't normally produce flowers or seed underwater so it is being wasted in a tank with only a couple of plants. It could also be poisoning the fish if the levels get too high.

Most aquarium plants do well when given a liquid iron based plant food with trace elements added.

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What is the pH of your tap water?
If that is close to 7.0 I wouldn't bother adding the pH regulator.

 

[Essjay]

5 ml of tap water conditioner by API

Do you mean this conditioner https://www.apifishcare.com/product.php?sectionid=1&catid=19&subcatid=102&id=655

If that is the one you mean, you need 5 drops to treat 5 gallons of new water not 5 ml - that would be grossly overdosing.

 

[Byron]

I concur with what Colin posted [and essjay too]. And in addition, I would suggest you are adding too many chemical substances. Colin mentioned the potassium...this should not even be needed on its own, it would be better to use the Flourish Comprehensive Supplement which has all needed nutrients, but use it sparingly. There is also the pH regulator, this is not something you should ever be using with fish in the tank.

Any and all substances added to the water get inside the fish, and each one of these will impact fish. At the very least it weakens the fish and usually causes stress which only makes things worse still.

 

[ReMz]

Were any of these fish added to the tank within the last couple of weeks? I agree with Colin that it sounds like a bacterial infection.

Also, I would cut way back on the plant dosing. It probably is not needed of the tank is fairly well established. You could very well be compromising the immune system of your fish which has allowed an infection to take over. Only takes one fish getting sick for things to snowball.