pH plummet, super low kH from tap... need advice

Hi all,
I started a 37 gallon tank a few weeks ago. I used to have a tank years ago in NYC and really enjoyed it. I now live in Oakland, Ca and decided to try again. From the tap the kH is 1, my pH is really high. I remember my NYC days which had a nice kH and a pH close to neutral from the tap. Now my tank has cycled and I was using pH 7.0 (that seachem additive) because my lfs keeper suggested using it. Now forgive me but when I started this new tank I was very rusty and just followed my lfs advice. Well after cycling my pH plummeted to 6.0. My fish are ok but this is not acceptable. I decided to check my kH and sure enought it has no buffering capacity. So I got kH buffer. The next morning my pH was around 6.5 and kH was about a 7. This is a radical shift and hopefully my fish can handle the swing. I just wonder if anyone has advice on stabilizing my pH and kH. Is the buffer the way to go? My tap water seems to need some chemical love to be usable for a fish tank. Any ideas or advice is greatly appreciated.

-AD

Hi,

Age: Tank has been up for 6 weeks
Filter: Eheim Ecco canister filter
Cycle: fish cycle, added bio spira to help accelerate
Current readings: (sorry no gH or Nitrate test as of yet)
pH: 6.5
ammonia: 0
kH: 7
nitrite: .25
Only additives are Prime and alkaline buffer

Tap water after 24 hours:
pH: >8
ammonia: 0
kH: 1
nitrite: 0

Fish:
Dwarf Guarm, 2 Rosy Barbs, 1 Red Tail Shark, 1 Cory, 1 angel
no symptoms all fish seem fine

My tap water does not see like something I would want my tank to emulate
Basically what I am asking is whether using the alkaline buffer is a good enough tactic for stablizing pH .

Thanks,
A

Ok,
Like I said, I am using no other additives other than Prime and the buffer. I really don't think a high 8 pH and a kH 1 is a good basis to emulate because that low of a kH will cause huge pH shifts and with a pH that high the plummet would could go from 8 to 6 quickly. As I remember pH is logarithmic. Yes, fish don't know what pH is but they know when there is a huge pH shift. I am sure the nitrites are at .25 because it is still a young tank and finishing cycling. I have been doing 30% water changes every week. The ammonia-nitrite-nitrate cycle doesn't just happen once, it continues repeatedly with each subsequent cycle yielding lower ammonia and nitrite until about week 7 or 8. So I am not too worried about the nitrite level. I am just concerned, like I have stated in not wanting to have my fish endure such radical shifts in water pH. What benefit does crushed coral have over the alkalinity buffer? It seems like a better choice because I could just take the coral out if the kH got too high. How fast does it effect water chemistry?

Thanks for any help,
A