Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

I've had a lot of help with this from a question I posted on a recent photo upload, but now I think the discussion is getting to the size where it really needs it's own thread.  Here's a LINK to what's already been said.  Thank in advance for all your help.

Background: Our aquaponic system is located at a local high school.  We have 50 peppers, 100 strawberries growing in clay beads, and 10 goldfish living in two 100 gal reservoirs.  We started off with more fish, but after a few attempts we decided to be content for the time being with the 10 survivors.  Our pH generally runs between 7.3 and 7.6.  It's a little higher than I'd like, but the water was resistant to being altered by neutralizers and pH lowering products.

Problem: Two weeks ago, I cleaned and calibrated our Hanna meter.  I verified the efficacy of the meter with a manual water test kit.  The TDS was reading below 200, so I added about an ounce of an organic liquid fertilizer (more info about that product below) to the reservoir.  I've done this before, and this has had a negligible effect on the pH.  That day, as soon as I added the fertilizer, the pH jumped from 7.4 to 8.1! 

Treatment: Since then, we've gone through two bottles of "pH Down" and the rest of our water neutralizer.  When we add the pH Down, the pH will drop from above 8.0 to about 7.6 immediately.  Within an hour of application, the pH will begin to climb.  Within 3 hours of application, the pH will be back where it started.  I spoke with the company that makes pH Down, and their advice was to continue adding the product until the pH actually stays down.

Tests: Based on a suggestion on the photo (link at beginning), a did a "vinegar test" of the clay beads the plants grow in and of the aquarium rocks that line the bottom of the reservoirs.  Neither resulted in any bubbling or frothing when added to the vinegar.  Earlier today I also did the following tests:

- Ammonium: 0 ppm

- Nitrite: 0 ppm

- Nitrate: 20 ppm

- TDS: 380

- Temperature: 88.0 F

- Water Source pH: 7.0

Fertilizer:  Since the spike occurred at the exact moment I added the fertilizer two weeks ago and hasn't come down since, it seems that more information about the product I use would be in order.  

The fertilizer is Fox Farm "Grow Big" Hydroponic Liquid Fertilizer: . Until this last application, adding fertilizer had an insignificant effect on pH.

Although our TDS was low when we first started the system, and although "Grow Big" is an organic product, I was initially reluctant to add the product to the water with the fish. While the students were out for spring break, we wouldn't have access to take care of the fish.  We ended up taking the fish to our office for a vacation, and I tested out the fertilizer in the system before the break.  After the break the plants looked great. 

Come to find out, we had missed a fish who was doing really well despite going hungry for a week and living in the dark in water that had fertilizer.  Ever since then, I've added an ounce of fertilizer every time the TDS drops below 200.  But I would never apply more often than once every two weeks.

I'm really not sure what to do at this point.  The fish seem ok, but the plants are really starting to get stressed out by the high pH.  Thoughts?

Views: 1057

Reply to This

Replies to This Discussion

Hi Amanda.  I'm no chemist but I'll take the first shot at this.  (good idea posting something in the Chat room BTW).  This sounds like you are buffered up with an alkaline mineral, like calcium  this is the same thing that people with hard water like well water see... especially if the well is pulling from an area with limestone. Probably came in with that hydro nutrient. You will have a hard time getting this down as long as the mineral is in there pulling it up.  You might want to try a partial water change to dilute it.

Thanks Sylvia.  I'll give it a try and post back.  We did replace about 1/4 of the water when the trouble first started.  Do you think we should try to replace 1/2 of the water?

Hi Amanda. Does Hanna make a TDS meter that can be used in organic hydro/aquaponics?  Something with a double junction electrode might be the way to go when using organic nutrients or have "dirty" water (like an AP system). Otherwise the probe may not be able to give you an accurate picture of where you're at. This might be worth checking out with a phone call to Hanna to confirm your particular probe/meter is the right one for an application full such organic nutrients (fish poo and the fertilizer you are using.

Are you using a digital pH meter as well? Because they can be quite goofy in regards to organic matter in the water as well. (Usually showing/rising to an unrealistic ridiculously high pH). Try using an aquarium pH test kit (the kind with the liquid droplets) just to get a confirmation that, that (8.1) is in fact your actual pH. 

You didn't say how big those 2 bottles of pH down were...

It would be really good to confirm your pH with a regular 'ol liquid droplet aquarium test kit before you go on troubleshooting .

Hi Vlad,

Because the problems started after I cleaned and calibrated the Hanna meter, I, like you, suspected the meter was not reading correctly.  That day and several times since then, I've confirmed the pH accuracy of the Hanna meter with our aquarium test kit regularly.  We use a high pH test and a regular pH test.

The meter was given to us by our sister greenhouse in Paris, TN that they use for their aquaponic system.  I hadn't heard of any issues there, but I hadn't asked.  I'll call our sister garden and Hanna to confirm.  We also clean the probes every two weeks to every month.

Sorry, the pH Down bottles were only 4 ounces.  We're in the process of ordering the 16 oz bottles, but they're not available in-store.  It's also worth mentioning that I spent an entire day with my gps and a phone book driving to every aquarium and pet store in Knoxville.  When I asked for something that would lower the pH, the store was either sold out or they would try to sell me a neutralizer or conditioner.

So given that the liquid test kit is correct, the growing medium and aquarium rocks aren't alkaline, and other aquarium readings are normal, what would you recommend?  Continue adding pH down along with replacing some portion of the water?

Thanks for your help!

I suspect the pH rise will be because of one of two things.

A-your tap water is actually much higher pH than you realize (if you get a pH of 7 directly from the pipe, then it could easily be well over 8 once the CO2 escapes, and this can vary through the year too.)  Bubble a jar of your tap water overnight and test the pH to know what you are really dealing with.

B-something in the fertilizer could be causing you issues, or perhaps it has caused an excess gunk up and now you have an anaerobic pocket somewhere causing the elevation in pH.

Now if your tds meter for hydroponics is really managing to measure nutrient strength accurately, then you hydro nutrient isn't organic.  See TDS or EC meters for hydroponics simply measure the electrical conductivity of the nutrient solution and that is mainly affected by the mineral salts in the water.  Nutrient rich aquaponic water won't necessarily read much of anything even if the nitrate levels are quite high so a TDS meter or EC meter isn't necessarily a good indication of nutrient strength for aquaponics.  If you are adding something regularly that brings the reading up then you probably should be doing water change out's every so often to avoid imbalanced build up of nutrients the way they do in hydroponics.  I don't like doing water changes so I don't recommend adding mineral salts regularly.

I agree completely with Vlad and TC...the TDS meter isn't really telling you much.  I also advise not getting too carried away with pH Down as it has a bit of citric acid in there which won't be good for your system's bacteria in large doses.  Best would be to look for a more pure acid rather than a blend.  In order of preference I'd recommend phosphoric acid, nitric acid, or muriatic acid.  And be sure to remove the fish if you are messing around a bunch with the pH, just as you did with the hydro nutrients.  They won't be happy about wide, rapid pH swings...not even your hardy few that are left!

Hmmm...well so much for that idea...I thought maybe the slow build up of organic matter (fish effluent and your fert additions) were just making your pH probe give goofy readings in your system...

Fox Farm Grow Big Ingredients: Ammonium Sulfate, Ammonium Phosphate, Urea, Blood Meal, Potassium Nitrate, Potassium Sulfate, Earthworm Castings, Norwegian Kelp, iron EDTA, zinc EDTA, manganese EDTA, copper EDTA, chelating agent, Disodium Ethylenediamine Tetra Acetate (EDTA), sodium borate, and sodium molybdate.

Much of those items are 'highly' alkaline...though fox farms appears to make a pH adjustment to their product...

This is kinda weird, but one of the biggest complaints fox farm gets seems to get from folks is that their 'grow big' product lowers their pH way too farm themselves seem to be aware of this "too acidic" gripe/problem and address it on their FAQ page...

..."Both our Grow Big® and our Tiger Bloom® formulas include a concentrated micronutrient package that is low in pH.  The advantage to this is that a low pH enables micronutrients to remain stable without any nutrient fallout.  FoxFarm fertilizers are extra-strength, and plants can absorb them easily, but this can cause pH swings.  Regular pH adjustments are recommended especially in early growth stages.  As the plant ages, you’ll notice that the pH will eventually stabilize"..


Is that an organically certified product? or did the marketing wizards (after checking with the lawyers of coarse) just slap a "contains organic nutrients" slogan on there. Because there is a HUGE difference... in 'technical business speak' they are not lying (kelp and worm castings) even though their intentions for making such a statement, and such a statements effect on you the consumers mind were far from honorable...

I'm guessing they lower the pH of their product so much because of longer shelf life issues). I've only experience with various home made organic hydro nutrients and all of those are generally pretty high I don't know how such an adjustment may play out long term...though I have some ideas...

You did let the tap water you tested sit out over night, right?

If you wanted to continue to lower pH I'd use plain HCL from your schools lab if they have any. But...

a good idea might be to stop using the fox farm product and stop trying to adjust pH...teach your kids about rain water up with rain water...if there are fish in the system just carry on feeding them and paying close attention to water parameters, if not, then dose with plain ammonia and let the nitrification process take it's course and lower the pH by itself over time (since your media is inert and all). Maybe use a 'non-variable' product like MaxiCrop+Iron to keep the plants going. They look alright in the pics you posted. Hope some of this is of some use/helped. Good luck.

Oh yeah...copper and zinc seem like really bad things to be adding regularly to an AP system (one more reason to stop using the fox farm product)...and if you need yet another reason, EDTA chelates have been proven to be toxic to plants, which is why most serious/reputable hydro folks/manufactures/growers use the EDDHA or DTPA chelates...and have for some time now.

OK, it's been a month and it's time for an update.

I've vowed to stop putting in the organic fertilizer for two reasons -- we don't need them and frankly I don't understand at present how it's affecting the system.  I spent a long while reading the labels of all the products we were using, and realized that the water pH neutralizer works by removing ammonium.  Since we've stopped using that, the nitrate level has gone up to a sufficient range and there is no longer a need for supplemental fertilizer.

The pH has still been consistently between 7.6 and 8.0 this whole month.  The fish and plants are alive and growing.  The only serious symptom so far is nutrient deficiency in the plants, which is caused by the pH being so high.  We've slowed down on adding pH Down for aquariums since I learned from Sylvia Bernstein's guide (and her post!!!) that it contains ingredients that may not be best for the system.

This week, I finally found out the cause (I hope)!  The aquarium rocks in the water reservoirs passed the vinegar test and shouldn't be raising the pH.  But, this is a public school and the rocks had been used before (of course they were cleaned, etc before we put them in the tanks).  There are a small amount of seashells in the rocks!  I spent some time yesterday sifting through all the rocks and found a handful of seashells.

So my question to you is this -- How many seashells do you think would be responsible for raising the pH of our 200 gal system by 0.5 - 1.0 after 3 months?  We don't have the cost of replacing all the aquarium gravel in this year's budget (which has been drastically cut).  The gravel has been very beneficial in the tank, and I'd hate to get rid of it.  It holds the fish debris down and apparently the nitrogen fixing bacteria live in the gravel and media.

My second question is How long should it take before the pH starts to drop after we remove the seashells from the system?  I'd prefer not to replace water for reasons that include the chlorine from the tap will kill the nitrogen fixing bacteria, I don't want to add more water conditioners unless we have to, and replacing the water quickly would shock the fish because they're accustomed to a higher pH.

Thank you for your help!

You said your gravel is in the fish tank?

I generally prefer the gravel be in the grow bed for a media filled grow bed or a separate filter since in the bottom of a fish tank the gravel may collect enough solids to create an anaerobic area that could actually cause an elevated pH and could also offgass some nasty stuff that would be bad for the fish depending on how the system is set up and how often you vaccuume the gravel out.

My personal experience with sea shells... They generally only buffer to a pH of 7.6 or at least that was the case with the ones I  had in my old system (about 40% of my gravel was shells), my pH would go up when topping up with lots of well water but would generally come back down to 7.6 as long as the fish were eating lots and the nitrification was working hard.  I had to supplement heavily with chelated iron.

If you need to do large scale water changes and your tap water has just chlorine in it, get a barrel and an extra aquarium bubbler and you fill the barrel with tap water and bubble it for a few days to prepare it for use in your system without needing to get water conditioners.  However that won't work for chloramine so you need to know what is used in your water supplies.  Beware the pH of your tap water, if you test it right out of the tap, you may get a false low reading but then when you test it after it has bubbled overnight in the barrel you will get a more accurate reading.  Bubbling the top up water in a separate barrel is a good place to adjust the pH (before you put it in the system.)  I like muratic acid for adjusting the pH before use in the system since bubbling the water will mix it and allow gasses to escape the hydrochloric acid won't cause anything harmful in your system used this way.

I doubt you need to do a complete water change though since if there are shells in there, the pH would just buffer back up even if your tap water is truly low pH.   If there is more than just a few bits of shell mixed in, you may not see the pH go much below 7.6 until all the calcium carbonate from those shells has been dissolved.

Hey TClynx,

Thanks for some really helpful information. I've read of people having issues with HCl but they were adding it directly to their system, not bubbling it in their top up water first. Would you recommend bubbling it for 24 hours or is a longer period required? From what I've found online (Here), it recommends 1/4 gallon to lower a 20,000 gallon system .1 ppm. I'm skeptical of any formula because I know it depends on what is in your water and also the temperature of the water, but it seems like a good place to start.

I plan to add 1/2 gallon of HCl to about 100-200 gallons of water and then add that to the system after bubbling it for 24 hours. Then test the ph the next day, rinse, and repeat until I reach 6.8-7. I'm shooting for a .2 pH drop each day, or changing the ph from 8.8 to 6.8 over 10 days. Do you think this is gradual enough?

My pH has reached 8.8 since I added gravel to the system, our tap is 8.1, and I need to do something soon for the safety of our fish and plants. Any advice would be greatly appreciated.

i agree with tc.. the gravel (with shells) didn't raise the ph up that high..

what's the expiration date on your ph test chemical bottle?  are you testing at the same time of day? (the ph will swing a bit on it's own in the system between night and day..)


the only thing i would "add" to the system would be maxicrop with iron - the ph will come down on its own

but i see that folks on this forum lean towards adjusting, and many have experience.. just make sure any changes are gradual.. i'd stretch the timeline out over a couple weeks (if i tried to adjust the ph)


Reply to Discussion


© 2024   Created by Sylvia Bernstein.   Powered by

Badges  |  Report an Issue  |  Terms of Service