Backyard Aquaponics
A place to discuss aquaponics

Hi Bridgie
That's curious about the rainwater changing pH to base. I'm also unclear why and how you are getting first wash rainwater? What is the roof which collects the water made from? Also I've never heard of an AP guru suggesting using pH Down before. I had been advised here in the beginning of my AP adventure not to use it, especially for the reason you mention, it will constantly need it until you figure out what is causing you rainwater to go base like that. Is there perhaps a polluter in the area which could be contaminating the rain? Is there something on the roof collection system that is affecting the pH? More often we see APers who use well water have this issue as the water was sequestered underground and away from oxygen then when it is exposed to the air it shifts to base by by a few points. What method of pH testing are you using? Have you tried another method?
I believe we can help you get to the bottom of this with a bit more information.
Brian

Sorry to create so many questions, but appreciate you helping me, boss!

I am using an API test kit - regular pH and High Range pH tests.

My rainwater is slightly acidic, right (pH 6.4)? With all of the limestone in the area, I thought the rainwater would be basic.



First flush (a 200 gallon tank) is supposed to remove majority of pollen, dust, bird poop, that collects on our metal roof during the first few minutes of a rainfall. After the first flush fills, rainwater collects in a 20,000 gallon tank. That water is pumped through a sediment, carbon, and UV filter when there is any internal house need. Between rains, I pump the first flush to a 305 gallon tank located near my AP system. I started using the first flush water nearly a year ago because 1) it's free of chlorine, 2) it has some inherent nutrients (though perhaps some pollutants!), and 3) I hate to throw out water (like in your area, it's a commodity).

Household water (filtered rainwater) is 6.0. Water in my top off tank (from the first flush) is 6.4. Water in FT is 7.8 to 8 (in the range of nutrient lock out). Any polluters OUTSIDE the system should be reflected in the top off tank. With the ongoing construction in the nearby area, including cutting of limestone, it wouldn't have surprised me if the top off tank pH was basic. The numbers, however, don't reflect that.

So, I'm left with a polluter INSIDE the greenhouse. I have some dutch buckets with soil, but the largest potential pH adjuster is the granite in the GB. That seems to be echoed by the water test - pH increasing from 6.4 to 7.8 in 24 hours with only the addition of GB granite.

I will try testing pH with a pool test strip later today. For the moment, I'm stuck believing that my GB media (granite) is increasing the pH to it's own equilibrium (which must be about pH .

Hey thanks for the answers Bridgie
Have you tested the granite using the vinegar test? Here is an example of testing for limestone in vinegar


What you are looking for is a chemical reaction to the acid in the vinegar to the rock in question. Perhaps that isn't granite after all?
Brian

No immediate fizz with the vinegar test.

I’ll rerun tests with pool test strips. It’s strange that pH rapidly increased in my top off tank and granite test. I will retest all water - in system and top off tank. My API test equipment (and everything in system except hydroton) is second-hand, so could be considered suspect. Are digital pH meters reasonably accurate?


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One additional note on vinegar test, agitating the granite does create some short mild effervescence and appears to lightly degrade the rock. If it’s local rock, I’d be surprised if there wasn’t at least a bit of limestone in a binder.

I’ll try my top off water with granite test again with different measurement equipment.


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Hi Bridgie
The pH meter I have I don't trust, but I think it is a matter of you get what you pay for and the one I bought I believe was ~$25
Does your meter have a calibrating liquid?
"Household water (filtered rainwater) is 6.0. Water in my top off tank (from the first flush) is 6.4. Water in FT is 7.8 to 8 (in the range of nutrient lock out). Any polluters OUTSIDE the system should be reflected in the top off tank. With the ongoing construction in the nearby area, including cutting of limestone, it wouldn't have surprised me if the top off tank pH was basic. The numbers, however, don't reflect that."
Yes that is odd. What water turnover rate are you using throughout the AP? How, I would wonder is there such a difference between those tanks with the water circulating throughout? Also I keep thinking the wash out water is adding some uncertainty to the stability of the AP.
You are probably correct about the stone media adversely affecting the pH. That seems a good place to start.
I hope this helps.
Brian

I completely emptied my growbed... finally. Dutch buckets, raft, and grow tubes are still hooked up. Yesterday, I measured pH in 150 gal fish tank at high end of range for API test kit (so probably 7.8-8. I topped off the tank with about 25 gallons rainwater (pH 6.4). Measured pH in FT after an hour or two - still at high end of regular pH test. Added pH down in about 20 gallons of fish water and mixed Into tank. After an hour, pH measured about 6.4. And all the fish lived

Measured pH this morning - back at 7.8.l?!?! I think the only possible contributor to pH could be soil in Dutch buckets (which I intend to convert to expanded clay media soon). I will take the buckets off line and use pH down again, and see if I can stabilize pH.


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Hi Bridgie. I have only stumbled across your blog today. It seems to be coming together well, despite initial problems, but isn't that how we get caught up in the whole thing? My systems use lava rock as the medium and it was initially quite high pH and was a battle to control for nearly 2 years. I added iron as a foliar spray to counteract lockout. When the pH finally dropped, it dropped hard and fast From 8 to 6.2 inside 5 weeks. I now have to regularly add base to keep pH in the 6.2 to 6.4 range. You may find the same further down the track. I would be surprised if your granite was altering pH as it is usually quite chemically stable (unless as Brian pointed out it may be marble or limestone?), but your reasoning re Dutch buckets sounds more like the culprit. As you say, soil in the area is mostly limestone, so likely the previous owners used local soil in the buckets.
Good luck with your progress and thanks for the pictures. Great to see what others are doing.

Thanks for taking time to read my woes, Nhibbo. I found a local aquaponics farm at our local farmers market, who seems to be using a similar granite without problem. I would love to put the granite back in the grow bed and avoid purchasing so much hydroton ($$$), but may first run a bucket test with rainwater and granite and see if there's any change in pH over a week. Removal of media gave me a chance to raise the grow bed about 5" and will make it easier to install a bell siphon.

Dutch buckets have been offline for a week. After adding pH down, pH has held at about 6.6 for 24 hours (whereas it previously increased back to near 8 within 24 hours after chemical addition). Will monitor for a couple more days.

Spring appears to have arrived in Texas, and the greenhouse was over 90 deg F today, so I'll have to pull the shade cloth back out soon.

My aquaponics system is still up and running, though supporting MINIMAL plants. The greenhouse remains pretty hot in the Texas summer. Several squash plants exploded in my grow bed, but died before giving any fruit - likely due to an uncontrolled infestation of white flies.

The biggest change has been adding a new outdoor fish tank (the above pictured rubbermaid 305 gallon) which is constant level. Fish tank drains to grow bed, and grow bed drains to sump. Pump in sump is on a timer. I fashioned a bell siphon, but it never worked - I suspect due to inadequate drain diameter from GB.

While I have not regularly checked pH, it seems to be holding in the 6.6 range. Ammonia is minimal, as are nitrites, but nitrates have exploded over last few months. I think this is due to two things - inadequate plants to process nutrients, and an algae build-up in fish tank. Now that my tank is outdoors, I'm having to determine the best cover for the tank. I've had two layers of shade cloth and an old bed sheet, but I think algae has continued with the indirect light. Tonight, I added two additional layers of landscape fabric, and it seems to be pretty dark now. I will monitor fish over the next few days to see that they aren't gasping for oxygen... I might add a third air line to the tank as a precaution as the algae hopefully dissolves.

Insulated enclosure and fabric cover for fish tank:


I have not brought dutch buckets back online, but hope to do it in next couple weeks as I push to get the greenhouse planted for fall harvest. I still would like to add additional filtration, but it probably won't happen in 2019.

After transfer of fish to the new tank, the system was neglected for about a month, with my primary focus keeping fish fed. Cleaning of a swirl filter was also neglected, and when I finally did so, I found two tiny goldfish (and a skeleton) in the bottom. They now live in my daughter's aquarium!

Fingers crossed for a productive fall with my aquaponics.