Originally Posted by squandel
Just a follow up... Tank looks great! Water has cleared up and it would seem that so far, the cycle I'm doing has worked fairly well. The only problem I've run into is the loss of 5 out of 6 Tiger Barbs. I've put in 4 Angels, 4 Zebra Danios, 4 Serpae Tetras and a Corey Cat (not all at once, mind you)which have all seemingly thrived but not so the Barbs. Water is still very high as far as PH but I'm working on gradually lowering it.
First off, welcome to Tropical Fish Keeping forum. Now to your issues.
The loss of the Tiger Barbs is a blessing in disguise. You have some very serious compatibility issues looming with your selection of fish. And the p|H adjustment may well kill other fish, I'll explain momentarily, but first the compatibility problems.
First, angelfish are slow, sedate fish with long fins. Tankmates have to be carefully selected, as many will find the angels' fins too tempting and start nipping them off, which is highly stressful to the angels and if allowed to continue the angels will almost certainly die from this. Also, fish that are quite active can stress out angels just by swimming around them.
Tiger Barb and Serpae Tetra are two of the worst fish to put in with angels for the fin-nipping aspect. Both these fish tend to be fin nippers at any time, even with each other. You can read more in our profiles. Click on the shaded name to see that fish's profile, it will explain all this. You need to remove these from the tank, return them, give them away, whatever.
The Zebra danio are too active to be in with angels; this applies to all danio species, and all barbs.
Fish that are under stress, even if nothing "appears" to you, will have weakened immune systems which makes them more likely to come down with other health issues, and almost invariably have shorter lifespans. No different than humans under severe stress.
Now for the pH. The pH of water is connected to the hardness. Carbonate hardness (KH) acts as a buffer to keep the pH stable, whatever it is in the tap water. Adding chemicals to lower it will usually not work; they may lower it briefly, but as the KH buffers work to bring it back up, the pH fluctuates down and up, and this is highly stressful to all fish. If you can tell us the hardness of your tap water--and your water supply folks will know this, some have websites with the water analysis posted--we will be able to offer advice on how to lower the pH naturally and safely, if that is really necessary. It is preferable to select fish that will manage in your tap water, rather than adjusting tap water. And many fish that are commercially raised, as those you have mentioned are, can be quite tolerant, at least up to a point. I can go into this more when I know the hardness number(s).