PH level drop in 5 days

Question
I don't think accuracy is a problem with the test kit.  I have been cycling a 5 gallon "hostpital/fry" tank with food for about three weeks now.  It has a PH level of about 7.2, so I have something to check the test results against.  I have been cleaning out my test tubes with plenty of water rinsing and drying with a twisted paper towel.  No bleach, but will from now on.  What do you recommend on frequency of water changes?  And how much water to change?  I did a 25% water change tonight and it bumped the PH level to 6.5.  3 platies seem to be fine, 1 molly seems to be acting a little funny.  I might pull him out and put him in the other tank soon, it has pretty much cycled.  I have been syphoning waste off the bottom every other water change.  I realize that some waste is needed to produce ammonia for the tank to cycle properly, so I leave some in there.  I don't have any driftwood or bogwood (I don't know what bogwood is) so that isn't the problem.  All plants are plastic, I have a ship and a skull that I believe are plastic too.  I have about 2 1/2 to 3 inches of gravel on the bottom of the tank.  Any advice you have, I'm listning, or reading in this case.  I had a few fish in the past and they died because I didn't research what they needed for a healthy enviroment.  I don't want that to happen again.  My wife laughs at me because I'm always lugging buckets of water, buying stuff at the pet store, twisting up paper towels in little glass tubes and watching the fish for hours.  She says they're only a $1.49 each.  But these little guys are my pets, my 7 year old son and I named them all.  So I want to keep them as healthy as possible.  There was a time when I thought all you needed for fish was water and to feed them occasionally.  Not the case at all!!  Thank you again for all your experience and taking the time to share it.  Matt
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Here I go again.  I am using an airstone.  How much should I change the water?  I've been doing a 25% water change about every two days.  Is that too much or not enough?  What is an acceptable PH range?  I've read that livebearers thrive at 7.5 and that a variance of 1.0 up or down is acceptable.  Is that true?  If so, how are they doing so well at 6.0?  I'm sorry for all the questions.  There is a boatload of info on the net about aquariums, but everyone seems to have different opinions.  The only reason I'm harrassing you is because you seem to make the most sense out of everything I've read.  As always, thanks a million.  I'll bug you later with more questions when I think of them.  Matt
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I feel like a pest asking so many questions, but I have another one for you if you don't mind.  My ph level has dropped from 7.1 to 6.0 over just a few days.  I think it's been about 5 days since I last checked.  Is this possible or am I getting false readings somehow?  I checked my tap water and it's around 7.3 - 7.5.  I have been adding Ammo-lock since my tank is still cycling and Melafix because I'm not sure if the fish have a bacterial problem or not.  Is it possible I'm getting false readings because of these two things being in the water?  I did a 25% water change last night but didn't check the level.  I've read that drastic ph changes can be fatal to some fish, so I find it hard to believe that it changed that much and the fish are fine.  If the reading is accurate, what causes it to fluctuate so much?  By the way, I'm using API's freshwater test kit, the dropper kind.  As always, thank you for your time and knowledge.  It is much appreciated.  Matt
-----Answer-----
Hi Matt;

No problem! It's what I'm here for!

Just keep doing water changes. It mat still be pretty unstable and that alone can cause pH to bottom out. Add more circulation to the water too. Use an airstone powered by an airpump. I have found it to be very valuable in tanks with a lower pH. More oxygen tends to help the system stabilize during the break-in period. The beneficial bacteria needs oxygen too.

It's actually not a bad thing to have a lower pH during the break-in period. Ammonia is far less toxic to the fish when the pH is under 7.0. If you are concerned about whether your test kit is accurate, take a sample of water to the local fish store to get a second opinion. It's worth a try just to be sure.

At Your Service;
Chris Robbins
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Hi Matt;

You aren't bugging me. I live for challenges like this. ;-)

Check the accuracy of the test kit. Also clean your test tubes or vials out. Residue can cause false readings. I use a mild bleach solution and a tiny strip of a rag or something to clean mine. Cotton swabs can work too. Twist it around in there with the bleach and water really well and rinse, rinse, rinse.

Your fish are used to the pH the tank is now so they are fine. Make sure there isn't a lot of waste in the gravel too. It adds to the acidity. I can't remember if I asked about driftwood or bogwood before, but do you have any in the tank now? If not, good. If so, get it out. It causes the pH to drop.

If the pH drops lower than 6.0 we might need to buffer the water with an additive but it's risky. It's best if we don't need to. Just keep the waste matter down, keep it oxygenated, and double check the test results.

At Your Service;
Chris Robbins  

Answer
Hi Matt;

Yeah, being laughed at is a common plight for the dedicated fish hobbyist. Been there myself more times than I would like to admit.  ;-) It's hard for other people to relate to pets that aren't "cuddly".

I wish I had more information for you on the pH. I really think once the tank finally balances it will probably be fine. Avoid making too many water changes so there is a bit of ammonia and nitrite in the water for the bacteria and keep lightly vacuuming the gravel. It will just take time.

Let me know if anything else comes up or you need more help....

At Your Service;
Chris Robbins