Sudden ammonia spike

[KariC]

Hi All, relatively new tank with sudden ammonia spike that I can't fix.
Tank set up in February, a fluval 23 gallon with a 20 gallon HOB aqua clear filter, gravel substrate and mix of live plants and fake. Let tank cycle, slowly added fish. Had 3 guppies, 6 tetras, one pleco and one pictus catfish. All was going great, everyone happy, plants growing, clear water, good water parameters (api master test kit). Then.... had an algae bloom three weeks ago. First lost guppies, then pleco, then catfish. Tetras are still alive. Did some water changes, vacuumed gravel, algae went away. Ammonia spiked and can't get it back down. Been doing water changes every 3-5 days, approximately 50%, adding ammonia lock. Ammonia remains .5ppm, nitrite 0ppm and nitrates between 20-40ppm. Last week did a dumb thing and changed foam media in filter. Added some aqueon PURE live bacteria and enzymes last week too. Also API quick start with water changes. Been at this about 3 weeks now with no change in ammonia and nitrates. Ideas?

 

[Deleted member 149562]

Ammonia lock is bad for the water chemistry as it kills the food that the newly established filter bacteria need to get rid of the ammonia that the fish produce

By using the lock, you may have restarted the cycle process depending how many times you used it and in what dosage

 

[Slaphppy7]

By "Let tank cycle", what do you mean, exactly? Fishless cycling is an active process, it doesn't just "happen" on it's own.

What kind of water conditioner are you using? Have you tested your tap water for ammonia?

 

[Colin_T]

Do a 75% water change and gravel clean the substrate every day until the ammonia and nitrite levels are 0ppm.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Reduce feeding to once a day until the filter has recovered. This might take a month due to you replacing the sponge. If you kept some of the filter media, then the sponge should be colonized by beneficial bacteria sooner.

You can buy liquid filter bacteria supplements from most pet shops. I don't think you really need them but if you want to use them, I recommend a double dose every day for a week and then pour the remaining contents into the tank. Try to add the bacteria near the filter intake so it gets drawn into the filter where it belongs.

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How often do you clean the filter?
How do you normally clean the filter?

Don't add any more fish until things are back to normal.
Don't add another pictus catfish. They need to be kept in groups and can reach 8 inches long, and they like small tetras.