pH is dropping.......WHY!?!?!??!

[Impaler]

Help! I noticed my two hitchhiker mushrooms over the past two hours suddenly shrivel up and withdraw for no apparent reason. That set off the little internal alarm to do a full barrage of tests. The only think I've done lately is add 20# more live rock last weekend. I've run the tests twice since then with no appreciable changes noticed.

20gal, 15 gal sump
eheim, gutted, running as return from sump
200gph powerhead in tank
Nitrate, ammonia, nitrite, phosphate, all 0.0
Calcium is holding at 450. had been dosing with Kent liquid Ca. to bring it up from 250. Did that over the last month.
2 damsels, 1 neon pseudo.
no skimmer
150 watts pc, plus 40 watts actinic.

pH has normally been b/t 8.0 and 8.2..........it just tested at 7.8 or maybe lower.

Any ideas? This is starting to worry me. Thanx
Dan

[Physh1]

I would venture to say the 20 lbs of live rock and no skimmer led to a slight rise in organic waste in the water. I would check your alkalinity and i would bet to say it will be a little low. A water change may help also. If you need to add some alk buffer. That will help stabilize your lower or fluctuating ph levels....

Your alk should be 2.8-3.2 or so...or if you go by hardness a level of 8-10 is good. Having levels lower than this can cause your ph to fluctuate a little more than some feel comfortable..

Good Luck...:)

[tyoberg]

What's you alk? If you're messing with your Ca++ you should also be keeping an eye on your alkalinity. If it's less thatn 2.0 meq/l, that's probably your problem.

Ty