Backyard Aquaponics
A place to discuss aquaponics

NO....

I'm at work for the next 2 days, won't be home till Wednesday and I'll give that a try. I'll abubble off some tap water, take a reading, then add some HCL and see what happens overnight. I'll also try and crush up some of the cinder and let it bubble overnight and see what my media is doing to the water.
Probally be the weekend before I can post my results, but I'll let you know what I came up with.

Cory

Okay I got away from work long enough to go and do some testing a get some water samples.
Last night at 6pm my FT water was at 8.2, all other readings 0. I took a bowl of water off for later experiments, then added 5cc of HCL to the FT. Retested the FT an hour later and the pH was at 7.4-7.6, it read at the end of the scale for both normal and high pH tests. Came home this morning and tested the FT it had risen to 7.8 in about 14 hours.

In the bowl of water saved, it was also at 8.2. I crushed up a heaping tablespoon of my black cinders (scoria) and mixed it into about a pint of water. Didn't have an air stone at work but I kept stiring it whenever I would pass by. Tested it this morning and it was still 8.0-8.2, not much change.

Comments? Conclusions? Suggestions?

Cory

If the media buffers the pH then 8.2 might be it's buffering point. Since you can adjust the pH try bringing it back down and then isolate some water from the tank. Wait an appropriate time and check if it is still down, if it is add media and test it later to see if has changed.

I don't think it is the media buffering the water. I think its whats already disolved in my tap water that is bufering. Plain tap water thats offgassed for a day reads 8.2-8.4

Interestingly I just looked up our county 2008 water report for my area the report says our water is supposed to be 7.4-7.8, a hardness of 60-190, nitrates of 2.4-2.7, and trace of chromium and copper.

Cory

If you are testing your media for pH, it would make sense to start with a neutral 7.0 water, either pure rain water (not acidic rain water) or distilled water that you can buy in gallon containers at your local store. Then you can definitely tell if your media is pH inert or making the water more alkali. Having said that, however, your water source is most likely the culprit. Unfortunately, I will face the same problem as you as my water source is also high in pH, so adding a buffer may have to become part of your routine. And as you have heard before, the natural cycling in AP systems does lower the pH eventually- the reason why is that the bacteria uses the alkali to break down the ammonia and nitrites. It takes a while but you will probably never see a pH reduction because you are constantly buffering your water higher with each top up.

Ok lets see if we can work this one out. I have two identical systems one has been running a couple of months longer than the other. I am using red scoria as a medium. In one system I have lots of plant growth in the other relatively little. I had an original pH of 7.4. I have adjusted the pH down to 6.6 over a number of days. And have re checked it every 2 days in the one with less plants it has remained at about 6.7 in the one with lots of plants it has risen back up to 7.4 within a week. So why is the plant filled bed rising in pH? It is obviously not the media or it would be happening in the other one as well.

I admit that my strengths is knowledge of the fish side of things as well as the science- the plant side of things are my weakness at this time- but is it possible that the plant's roots are competing with the bacteria for the available space in the grow beds? It would create smaller colonies of bacteria, which would feed on less alkalai than the other bed and over time show the difference in pH. It is just a hypothosis. Perhaps someone with greater experience could comment.

You also mentioned that one system was a few months older than the other one- there are other microscopic flora and fauna, besides the nitrifing bacteria, that creates what is known as the "growth factor", accelerated plant growth in more mature AP systems, even over hydroponic systems. Again, another theory but could explain the difference.

With the side by side systems where the one with lots of plants has a more quickly rising pH, it could be that the plants are taking up something that is leaving the pH higher. What sort of acid was used to adjust the pH? In Hydroponics phosphoric acid is used but I've seen the pH still rise again fairly quickly since I guess the plants are still using stuff.

Another possible variable in the side by side systems. More plants will transpire more water. So, if the transpired water was leaving the water with a higher concentration of buffering chemicals, that might account for the higher pH. Or anther possibility, are the systems automatically topping up? Could the top up source water be bringing the pH up? If so then the system with more plants transpiring water will cause that system to get more top up water and therefore have the higher pH.

Okay, I spent the last couple day lowering the pH of my 8.0 FT, using 5cc of HCL each morning. It appears that 5cc of HCL will lower the pH about 0.2 - 0.3 points. This morning I tested my system and it was at 7.2 after 3 doses, put in another 5cc of HCl and an hour later it is now at 7.0

I have to go to work over the weekend, so we will see what happens over 2 day without any HCL. My gut tells me I'm going to be right back up at 8.0.

On a side note, how do you test the pH of water that is discolored? I was going to test some of my local river water just to see what its at, but it already has the brownish tinge to the water and I couldn't tell if there was a color change, it was already the color of 8.2 on the colormetric card. I was able to test a clear fresh water spring way up in the mountains and it tested out to 7.4, unfortunately there is no way of getting that water to my FT except by carrying 5 gallon buckets at a time.


Cory

If your pH is around 7.x.... and you retest in a few days... without adding anything to your tank.... then it must be your media.. or your growbeds that is buffering it back...

I think this is true only if the buffering effect of the initial water hardness has been overcome.
Because the water in the area has a hardness of around 180 which is on the very hard end of the scale for domestic water supplies it has a high buffering effect on its own and will naturally return to a higher pH after an addition of acid as the carbonate and bi-carbonate are slowly converted.
see this quote ( from http://www.aquahobby.com/articles/e_adjusting_pH.php )

"Lowering the pH is a more extensive task. If you simply add a product such as “pH Down” this will not work. Your buffering system will simply very quickly raise the pH back to its original state. You must remove the buffering ions from your tap water so that you may lower the pH. The best way to accomplish this is to purchase a Tap Water Purifier unit. These units filter the water from your faucet using an ion exchange resin. The resulting water is free of the salts and minerals which buffer your water. This is the only reliable method I know of to reduce the buffering ability of your aquarium water and to lower pH. Without purified water, you may be able to lower your pH for a day or two, but without first removing the buffering ions your pH will climb again to natural levels. This fluctuation in pH is much worse than having the wrong pH to begin with." END Quote

The difference in the two systems may be caused by the nature of the Hawaii water supply - it is my understanding that while a majority of the water supply comes from underground with the consequent dissolved minerals, at certain times of the year there may be a lot of surface water in the supply that will be very soft and so respond to the CO2 in the system with a slowly lowering pH.

A Total hardness test kit will tell the story and let you know if it is possible to move the pH lower with addition of acid.

John

What do you guys think of these two ways to lower pH...

Filter the water through a barrel of peat moss?

Fill a carboy with sugar water and yeast. Stopper the carboy and attach a hose. At the other end of the hose attach an air stone and drop into your fish tank. The byproduct of the yeast eating the sugar is alcohol (stays in the carboy) and carbon dioxide which should create more carbonic acid in the water and lower the pH... sort of like algae respirating at night.