Join Date: Sep 2008
Location: Mt. Hood, Oregon
In my tank, ADA AS brought the PH down low enough that all the ammonia was converted to ammonium which is harmless to fish. I've added new AS to an existing tank and not had any problems. My PH is very low with AS: my tap water is 7.2 but my tank is below 6. Please take this with a grain of salt, as I don't know if everyone experiences the extreme PH drop as I do. I've never found the low ph to be a problem, but I only keep fish that do well in soft, acidic water. I see you have angelfish, and they will thrive with the AS, but who else is in there??
If the AS drops your PH below 6, the traditional ammonia tests will no longer be accurate. They don't distinguish between ammonium and ammonia so you will continue to get high readings even if there isn't a problem with your water.
Full disclosure: I do not have a chemistry background. I only know about ammonia vs. ammonium through internet research from possibly dubious sources. However, my own experience leads me to believe that this information is correct
The first time I upgraded to AS, I left some flourite in as a bottom layer. Just like you, I was hoping to maintain some of the bacteria load. Now, whenever my loaches do a bunch of digging (those little rascals...) pieces of the red flourite start appearing in my nice, dark AS, and I hate the way it looks. If your current substrate is a different color, you will probably have the same problem.
I think your tank already looks great. It sounds like you're happy with how the plants are growing, so why do you want to tear it all up to put in a new substrate? If I remember correctly, Tom Barr, the planted tank guru, says that AS is great for beginners because it makes the process easier, but it really isn't necessary if you know what you're doing. I think you probably fall into the latter category.
Maybe you should talk your wife into letting you get one more tank, instead!