PH\Cycle Problem

[senegal927]

Hello all

I just got a 40g tank all setup a week and a half ago with four pristella tetras. But am having a problem keeping the PH up. I've done water changes (30%) three times so far and I manage to get the PH up to 7.8 but the next morning it will bottom out to 6.0. The API test kit i have shows 6.0 as the lowest possible reading. So it may even be lower.

So my problem is I am not sure if my tank is cycled or semi-cycled due to the low PH. I say that because I know nitrifying bacteria stop reproducing once you go lower then 6.8PH. I also don't know why my PH keeps crashing. Also i think the ADA is still leeching ammonia so i'm scared to add any more fish. Based on my log it looks like a semi cycle went through and it's just left over ammonia from the ADA. Anyways any tips or advice is much appreciated. My plan is to eventually put in some Apistos!

Equipment/Setup
ADA Aquasoil New Amazonia
1 inch of sand under the ADA
Coralife Aqualight 18w T5's x2
Two large pieces of malaysian driftwood
22 plant cuttings planted (medium planted tank)
Aquatop cf-400UV canister filter (with seeded material)
Skimmer hooked up to a small powerhead.

[B]API Test Kit Reading
Day PH Ammonia Nitrite Nitrate

2 6.5 5.0 0.0 0
5 7.8(Water Change) 4-5.0 .25 0
6 6.0 2.0 2.0 0-5.0
7 7.8(water change) 1.5 .25 0-5.0
8 6.0 1.0 0.0 0-5.0
9 Just did a water change so i'll wait to post tomorrow.

Everyonee loves pictures! I was messing with the skimmer which is why you see lots of bubbles. [/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/SIZE][/I]