Nitrite Spike from Ich X

I had a bad case of ich on my tank so I dosed Ich X into my 75G tank. Unfortunately my dog had chewed on my siphon so I decided to treat my tank while I waited for my new siphon to be delivered.

It took 5 days for the siphon to come so I was adding Ich X to my tank without the water changes. Ich was all gone by day 5.

A week and a half later, I had 5 fish deaths not related to ich - the fish that died looked like they might have gotten dropsy. So I tested my water and found out my nitrites were way off as they were unreadable - hard to read from the API color page but it was so purple it's easily between 1 ppm - 5 ppm. Ammonia was 0 ppm and nitrate was 5< ppm.

I've been doing daily 50 - 60% water changes for the last 3 days and I have been able to drop it to 0.25 ppm but it now peaks at around 0.25 ppm - 0.5ppm by the end of the day. I'm also using seachem prime 2x dosage during water changes to detoxify the nitrite.

The tank was cycled, so was it the Ich X (malachite green & formalin) without the water changes that killed my bacteria?

Should I keep doing daily water changes or should I let the nitrite peak so the bacteria become established?

How much ppm is too toxic for the fish to handle?

 

What was your nitrate levels before this nitrite spike?

 

What was your nitrate levels before this nitrite spike?

I have a planted tank so after my tank was cycled I was getting 0 ppm ammonia, 0 ppm nitrite, and <10 ppm nitrate.

I would only do 1 water change a week

 

If the instructions said to do water changes there was probably a reason.. I would assume that the malachite green had some effect on your cycle. Just keep doing what you're doing though, you're handling it perfectly. You should see things back to normal soon

 

Formalin and malachite green can both destroy bacteria. I would keep up with the water changes to protect the fish and reduce the formalin / malachite levels. You could add more bottled bacteria to speed things up. Treat the tank as uncycled until things return to normal.
In future I would ditch the meds and treat ich with salt and heat. The chloride in salt also reduces the toxicity of nitrites so a little salt may help until the bacteria catch up