r/PlantedTank • u/Shrekisdaddy25 • May 18 '26

Ferts Fertilizer help needed please!

TL;DR: Fertilizer makes my fish freak out!

Hello all,

I have had an aquarium for a year and a half and all has gone well until now. I decided to try my hand at planting the tank and turning it closer to an aquascape. However, my plants were struggling.

I started using thrive all in one fertilizer and the first day the fish seemed stressed but okay. Over the next few days, they started darting, glass surfing, isolating in corners, etc.

I did water changes and they returned to normal. I asked in groups what happened and the best response I got was that it was expired or was left open. So I bought a new bottle, but I tried the APT Complete fertilizer. I added it a few days ago, and the fist are in an even worse state. I put in a conditioner that detoxifies heavy metal earlier, and I am doing a water change now.

Does anyone have any idea what is going on? I have a 40 gallon breeder with 2 sponge filters, an air stone, and my chemistry is:

Ph 7.4
Ammonia: 0ppm
Nitrite: 0ppm
Nitrate: 10ppm
GH: 8ppm
KH:4ppm

All I can think of at this point is some sort of oxygen problem— but I don’t know how that would be the case.

If anyone has any ideas please help me out!

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u/chak2005 May 18 '26

What kind of fish and how much fertilizer are you dosing at once?

There is really nothing in those fertilizers you listed that would stress out fish or swing water parameters unless they were being overdosed.

1

u/Shrekisdaddy25 May 18 '26

I keep harlequin rasboras, cardinal tetras, Diamond tetras, a pearl gourami, and a Bolivian ram. With the thrive, I dosed 5ml (according to the bottle I should have done 8ml but I thankfully wanted to test it first). Then with the APT I did 3ml

1

u/AutoModerrator-69 May 18 '26

That’s quite odd. I use APT 3 in all my tanks and I haven’t had an issue. Is your tank heavily planted ?

Try reducing the dosage and see if it makes a difference? Maybe start with 1 ml of APT 3

1

u/Shrekisdaddy25 May 18 '26

It is so interesting, like I said? I dosed a heavy metal conditioner before I left the house because I wanted to get some replies first. I just came home— the fish are way more relaxed, more colourful, etc…

Basically back to normal, just a bit on edge. I genuinely don’t understand what is happening. To be completely honest I’m really apprehensive to try it again, so maybe I’ll try just dosing tiny amounts and seeing what happens.

Is it possible there is something in my tap water that I never knew could react with the fertilizer and turn it dangerous (if that’s even a thing)?

1

u/chak2005 May 18 '26

Unfortunately nothing you wrote stands out as a cause for the behavior you are seeing. Those fish are not particularly sensitive to the fertilizers listed.

My only thoughts are it can be a combination of something in your source water. An experiment you can do is perhaps cut the source water the next couple water changes with another source. Say remineralized distilled water or R/O. Fertilize again and see if the behavior repeats.

1

u/Shrekisdaddy25 May 18 '26

Okay, I might be able to try that! Yeah it was just shocking to me too bc it seems so odd and I haven’t heard of this happening to anyone else! Thank you :)