Fresh2o
Aquarium Advice Addict
My 2 cents. There might be something in the gravel or the gravel itself. In April I setup a new tank with EcoComplete and was planning to do a fishless cycle. Well, ammonia was +8.0 ppm (I did not add any ammonia). 90% WC, tested ammonia (0.25-0.5), 8 hours later it was > 8.0. Was doing daily 90% WCs and getting the same result over a week. Ended up tossing the gravel, cleaning the tank and starting over. Did not reoccur.
Not saying that you should do the same, just something to consider.
Not saying that you should do the same, just something to consider.