pour some water into a tub. let it sit for 2-3 days and then check the pH. check again in 2 more days. Are they the same?
do the same with some of your brita filtered water. does the pH of each test specimen match? also, on your tubs you're taking measurements on now, just let one go (don't add any more pH down) and see where it and how long it takes to stabilize.
It sounds like you've got some kind of mineral overload thats trying to keep your water alkaline.

Thanks grizzman. I will let it sit and see what happens.

If the pH rises again i am going to tear everything down and wash it.

I did not wash the baskets the clay is in and i did not wash the white styrofoam boards that are floating. So maybe there is something on them that is causing the pH to rise.

I think in my book it says to use hydrogen peroxide to wash out the tubs. Is there any other cleaning solution i should use?

You mentioned using nutrients for hard water which makes me think you are using hard water for your system. This is probably what is giving you the rising pH, to some extent I think that is just the way it is with hard water and Hydroponics. (In Aquaponics the buffering of the hard water is desiried, needed and often not enough.)

In your testing of the water supply. Here are some other things that might be useful to know. When the water first comes out of the tap, it may have a different pH than it will after being aerated. This is because there is likely disolved CO2 in the water which will act as a weak acid. For instance, my well water when it comes out the tap will read a pH of close to 7. After letting it sit in a container with an air stone running in it, it will read a pH of 8. WOW that is quite a difference. I had not originally known that I should bubble the water before testing the pH and I was so confused about how my pH kept climbing when the tap water tested as 7.

So, I don't think the pH problem is one of cleaning.

I actually took to using rain water for my Hydroponics. It also tended to test with a pH of 7 but it didn't have the amounts of calcium in it that cause the to keep trying to climb. That way I was able to avoid daily pH adjustments.

Another trick that some might try is to use a naturally acidic media in part of the system. Perhaps something like coco coir or peat. I actually used wood chip mulch in my outdoor system to grow cucumbers that like a rather low pH.

Now I've been converted over to Aquaponics where the bacteria doing the ammonia-nitrite-nitrate conversion from the fish waste tend to cause the pH to drop over time so the challenge is opposite.

Here is a link that might be useful: My Hydroponics

Thanks for all of the help!

It does appear my pH is becoming more stable. The last 3 days the pH has stayed at 6.5 for tub1 and 6.9 for tub2. I have also started taking my measurments at the same time of day. I read pH will change during the course of the day.

I have about 5 more days before the lettuce sprouts are ready to put in the system so if the numbers staty stable i will use it.

I have heard of aquaponics and it is interesting, but at this time i want to keep things simple. I was at the pet store a week ago and did check out some of the neat aquariums they had. I could probably get into that hobby.

If you think Hydroponics has sucked you in, be ware of AP as it seems to become an obsession for many people!

Yes, pH will change through the day. Over night the plants will strip disolved O2 from the nutrients and there will be more CO2 in the water, causing the pH to be lower first thing in the morning.

Here is a link that might be useful: My Hydro

This may be useful although perhaps a little off-topic.

Here  in Africa  rain is at a premium, and many things are not readily available, so . . . we DIY a lot.

If tapwater is too hard and/or the pH too high we manage to deal with that with simple means.
Hardness is a result of the calcium and magnesium content of the water. It can be measured using a hardness tester bought at an aquarium shop. The test provides two measures:
GH (for General Hardness) is a measure for the total of calcium and magnesium content given in mg calcium oxide (CaO) per 100mL of water.
KH (for Karbonate Hardness) is a measure for the calcium and magnesium bicarbonate content. Also given in mg calcium oxide (CaO) per 100mL of water.
Naturally, the KH is part of the GH, and is always smaller, unless thereÂs a foreign bicarbonate in solution.
Bicarbonates are strong pH buffers which resist lowering of the pH.
The best way is to store the water under an aerator for a few days, and bring the pH down using a measured quantity of 5% white spirit vinegar. This will turn the bicarbonate ions into water and CO2 gas which will be driven off by the aerator. WhatÂs left is calcium and magnesium acetate.
Quantity: 0.4mL vinegar per Litre of water, per degree KH hardness.

Excellent information greystoke. I will give this a try!

thanks everyone - what a useful thread!

I tried 1/2 Tbspn of 5% White Vineager for my 9 gallons of water and it did lower the pH by .5, but the next day the pH rose back up .5

I undersand ph and how to read but do people really use vinegar and hydrogen peroxide to maintain there systems. If not how exactly are they used. Oh can somebody explain what the "zone" area is for on the thread post.

"zone" is the plant zone you live in. more relative to yard gardening that hydroponics. its an indicator of what kinds of plants can and do grow in your area and how well they do. basically has to do with high and low temperatures and statistical what not.