Do be careful with Ph Down Endgame. That stuff can mess up a tank really badly and cause a pH crash. One needs to know the gH
levels in the tank. If they are pretty high, you'll find using pH down won't make a difference. By adding more and more what will happen is it will cause the pH to not stay lowered, then drop suddenly and severely, stressing and likely killing the fish (fish do not deal with pH changes well at all). Also, Ph down contains a lot of phosphates, opening the door to algae. There are other, safer ways of reducing pH and gH
levels, such as using peat.
Do check out the following articles to get a better sense of pH, gH
and a pH crash:
aka Cycling Guru and the Ich Slayer
*glares at Terry and QTOFFER*
Card carrying member of FTAS & GCAS.