4 months ago my 20 gal was contaminated with ich leaving 2 angelfish and all natural plants. I treated the tank with ich tabs as directed. The water has been changed out several tines since then. Well over 50% water changes 3xs since. After 3 months i have added my first 3 new fish (a small breed plecco) 2 died the first day; the third died on day two. Now 4 months later i added several new fish. A school of tetra. Obe died after 2 hours. Two bala shark, both appear to now be blind and one of them is upside down as well.