Huge drop in PH level

Tracy Lee

Hello,
I have been doing aquaponics for about 2 1/2 years on a seasonal basis. I have a 200 gal. fish tank with 1 grow bed of equal size and a raft. Problem. I have filled my tank with well water. Ph at 7.2, 2 or 3 days later ph drops to 6.0. I have done partial water changes, same thing. Ph rises to around 7.2 then 2 or 3 days later 6.0. I drained my system last fall. Just restarted, all fresh water, same problem. My grow medium is expanded clay pellets and all tanks are lined with pond liner. Now 6.0 is assumed as that is the lowest reading on my API test kit. Any Ideas?

joc

Hi Tracey Lee. The pH should drop in a healthy system where the bacteria are converting the ammonia to nitrite and then nitrate, unless you're starting and top up water is highly buffered (ie. high carbonates >> 'hard' water) or you have alkaline media (eg. limestone). Don't do water changes, just regularly adjust your pH up with a little bit of lime.

I had some great advice on this from Gunagulla which I have copied for you below (see page 5 of my thread for more discussion)...

Quote:

Hey Joc, be careful if your pH test kit is indicating pH 6, as the pH can drop well below that and you can't tell with the usual test kit, which could make things difficult for the bacterial colonies in your GBs. When feeding the trout over 100g of pellets per day, I've found that the many kilograms of shell grit I have in my 1st system is not enough to buffer against the falling pH, so I use Calcium hydroxide = Ca(OH)2 = builders lime, and Potassium hydroxide = KOH. These are both strong alkalis, so you need to be careful using them, and they provide no buffering effect, but with careful use are great for controlling a rapidly falling pH. I alternate their use, so providing a balance of Calcium and Potassium for the plants.

Potassium bicarbonate, KHCO3, makes up 94% of the ingredients of Eco-fungicide, the other 6% is wetting agent/detergent, so I think it is best reserved for use as a foliar spray, although others have added it to their system water, apparently without any problems due to the detergent. I guess it depends on what quantity you use- but Eco-fungicide is a very expensive way to control pH in comparison with other methods.

I have been using dolomite to adjust the pH, but it takes a lot and it leaves sediment. It is also high in magnesium which is good for a bit, but would not want to overdo it. I am now using a settled solution of wood ashes (very strong), while I am waiting to locate some potassium hydroxide. I try to keep the pH at around 6.6 so that I can be sure I can read it properly and it gives me a few days before it drops back down to 6. Don't change it more than ~0.4 pH units a day as it may impact your fish.

I hope that helps :flower:

ebeuerle

Tracy,
Have you done a pH test on your water before adding to your system? I would recommend collecting about 4-5 gals and take a pH test on the collect water right after you fill the bucket. Then run an air stone in the water overnight and re-take the pH test. I suspect you may have a large about of co2 dissolved in your well water which would make the water acidic. This relatively quick test will let you know for sure. If you don't see a noticeable difference, I would do a hardness water test from API and make sure the well water has carbonates in it, if not you will need to add as suggested above. Potassium bicarbonate or hydrated lime will do the trick. Carbonates prevent large pH swings which can cause problems for fish and plants as well as the bacteria in your system.

Hope this helps!

Eddie

Tracy Lee

Some good ideas that i will check out. Ecspecially the water test after running oxygen in it. We have tested directly from the well and its 7.2. We filled the system, had it running a couple days with oxygen then added 150 1-3 " bluegills on friday and as of today close to half of them have died and we can't figure out why. Water temp is around 68-70 degrees.

ebeuerle

I wouldn't add any additional fish until you can get the pH issue under control. A swing of 1 pH is 10x (10 fold) change and can easily kill fingerlings. Also make sure your test kit hasn't expired to ensure good readings of pH. I would strongly suggest a hardness test as well to determine amount of buffer you might have in your system.

Tracy Lee

ok so we did the overnight test. Water was 7.4 when we put it in the bucket and 24 hrs later it was 8.4 so that is confusing. Would seem like there is something in the system lowering the ph that isn't present in the bucket. So last spring we started up the system, and the ph went up to 8.4 so we put in some ph down and then it went down to 6.0 and stayed there for the 5 months we had it running. We started out with goldfish last season and they all died, so we ended up putting some mid sized bass and bluegill in there and they lasted for about a month and slowly died off. We talked to a man who runs an aquaponics/brewery supply store here locally and he thought there could be something toxic to fish in our well water because he said goldfish are pretty tough and can handle ph swings pretty well. Will be getting our water tested but meanwhile is there something else that comes to mind that might help. Thanks

ebeuerle

Sounds like the co2 is off-gassing which would raise the pH. Regardless, that is a huge pH swing. I would recommend aerating your water before you add it to your system and if needed adjust the pH before you add it. A water test would also be recommended to make sure there isn't any other gasses that might be killing fish such as hydrogen sulfide.

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Huge drop in PH level

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