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PostPosted: Dec 3rd, '19, 15:11 
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350 gallon stock tank with hanging baskets with pH neutral aquarium pebbles under LED lamps (275w draw)
*I edited this to add that the water is running through a pond diy filter/sump container/container build pumped with two 1050gph pumps running through a container of sponges overflowing to second stage container with bubble aerated section containing about 15lbs of SUPER porous ceramic rock that is AWESOME stuff. Bacteria should thrive and help nutes to be more available. Pic added.

6.9 - 7.5 ph
11-13 GH
4 kH
API Liquid test kit with vials
Used potassium bi carbonate to feed plants / raise carb/bicarbs - to 4.
Added Iron Chelate EDDHA (the good kind) which is why the water is red tinted


Top up water contains Vitamin C powder enough to remove chlorines/amines and bring the pH closer to 6.9 in the main system.
Raw top up before adding is at 5.5 pH after sitting.


I've tried a few systems before and the mechanics are always fantastic but I can never get the water right. I decided to get a RO filter and now want to slowly taper the water in my 350 tub at a rate of 20 gallons a day with RO and Vitamin C powder mixed in to lower the pH that is currently at 7.6 until I add the powder and then it climbs back to 7.5 from 6.9-7 eight hours after adding the vitamin (ascorbicacid) treated water. I am concerned because I do not see the KH burning off like I've been reading that it should. Its still 4 degrees every time I test.

I have 4 varieties of cherry tomato growing and they seem to do well. Though the one that is flowering will have clusters of 14+ flowers only to have 3 left and now recently 0 left after they pollinate and then just flick off. There are about 15 healthy tomatoes growing though I am experiencing such high drop in flowers. Some will keep 3 tomatoes and some will drop all flowers.

I feel like the 4 degree kh and 6.5-7 ph rule in aquaponics is somewhat impossible seeing how as soon as you add any type of carbonate to the water for the 4 degrees you're supposed to have - the pH inevitably rises to a minimum of 7.2.

I think I covered everything, can anyone tell me why the pH is acting like it has a MEMORY setting?


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PostPosted: Dec 3rd, '19, 17:10 
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You are trying to deal in absolutes... and there are very few of them in aquaponics. You are going to end up with a brain hurt.

I've been at this for years and I've only ever measured KH & GH once, and that was just out of curiosity. The majority of people I know of that have taken to measuring KH, have ended up chasing their own tail around in ever decreasing circles.

I've never heard of the 4 degree KH rule. I've also never heard of adding vitamin C to RO water. It's usually added to water containing Chloramine. ie: scheme/municipal water.

Chloramine removal, without vitamin C, is much easier than many suggest. With aeration and exposure to sunlight/UV, it will disassociate and the resulting Chlorine will have gassed off within 48hrs.

I've also never heard of anyone using Ascorbic acid to reduce carbonate hardness. I'm sure, being an acid, it would to some degree. Hydrochloric acid is far cheaper, very effective, and is also beneficial for the fish.

Your pH is bouncing back up after adding it because there is insufficient acid to consume all the carbonates, so as the acid works on the carbonates, it dissipates and the pH climbs back up. It will take many additions of the acid treated top-up water for the carbonate hardness in the system to reduce to a point where your pH won't bounce back up.

As far as your tomatoes are concerned, it's likely there is insufficient essential flowering nutrients, ie Potassium, Phosphorus and Calcium, especially if you are removing the fish waste solids from your system via your filter set-up and also using RO water. It could also be too much Nitrate.

Collected solids should be treated in a mineralisation tank and the resulting nutrient rich water added back into the system. Ideally, and this is just my opinion, the fish waste solids should not be filtered out, but rather allowed to settle in the GB's, where natural processes, ie: worms, mycorrhizal fungi, bacteria, enzymes etc are allowed to break them down and liberate the mineral nutrients locked up in them. In a well designed, sensibly stocked system, it will take many years before the GB's require cleaning out.

One "almost" absolute I can tell you, is that RO water is not desirable in aquaponics. Dechlorinated scheme/municipal water is a much better option, as in most cases it contains carbonates and some Calcium.

The beneficial bacteria and most fish prefer a slightly alkaline water, and most plants will do perfectly fine with a pH up to about 8.0, or even slightly higher with the addition of a small amount of EDDHA chelated Iron.

That "Goldilocks" pH zone at around 6.7-6.8 is recommended so as to keep the fish, bacteria and plants happy, but you can run a system in the high 7's or even 8+ for many months and still achieve good plant growth. Don't be in a rush to force it down, unless it's excessively high, even then bringing down into the high 7's would be sufficient. It will drop naturally over time.

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PostPosted: Dec 3rd, '19, 17:25 
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So I realize in my long rants it's hard to follow exactly what im asking. ..lol so. .. The problem is I wanted to keep the pH to about 6.8 to 6.9. I was really only concerned about the KH levels not dropping because I was afraid they would suddenly plummet along with the pH which would probably kill the fish. I was thinking about getting some phosphoric acid or advanced nutrients pH down (55 phosphorus) for the NPK level. 85% food grade bottles might be better but I have no idea. I believe in the rule that plants need low pH to absorb certain important nutrients and stay balanced. But I also am very inexperienced in long-term use of any of these chemicals and their behaviors. Do you know if it is possible to maintain dkh 04 degrees for KH level at the same time as having a pH of 6.8 to 6.9?

I want the KH because at 6.9 I need a buffer to keep it steady from super swings. Sorry for all the edits im tired.


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PostPosted: Dec 4th, '19, 09:18 
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My suggestion would be to give yourself a range from about 6.1 to 7.2 for the pH and then use a mesh bag of some form of calcium carbonate. Crushed coral is what I use... Basically your pH should fall over time and the calcium carbonate source will slow this. Once this falls to around 6.1 or 6.2 you'd adjust the pH back up using potassium bicarbonate. The carbonates in both of these will help with the carbonate hardness (aka alkalinity) and should be all you need.

For a home system, It's really not necessary to watch the system too closely and it's actually not that easy to keep the pH locked down at a specific number. For a commercial grower it probably is a bit more important that they keep track of things because their livelihood depends on it. There is automatic dosing equipment that they might use (I tend not to trust this dosing equipment 100% because if a probe gets gunked up it can lead to problems - I learned this running research scale fermenters in a lab environment).

Hope this answers your question.


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PostPosted: Dec 6th, '19, 05:24 
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misterJOSHUA wrote:
So I realize in my long rants it's hard to follow exactly what im asking. ..lol so. .. The problem is I wanted to keep the pH to about 6.8 to 6.9. I was really only concerned about the KH levels not dropping because I was afraid they would suddenly plummet along with the pH which would probably kill the fish. I was thinking about getting some phosphoric acid or advanced nutrients pH down (55 phosphorus) for the NPK level. 85% food grade bottles might be better but I have no idea. I believe in the rule that plants need low pH to absorb certain important nutrients and stay balanced. But I also am very inexperienced in long-term use of any of these chemicals and their behaviors. Do you know if it is possible to maintain dkh 04 degrees for KH level at the same time as having a pH of 6.8 to 6.9?

I want the KH because at 6.9 I need a buffer to keep it steady from super swings. Sorry for all the edits im tired.

You're going to have a hard time trying to keep a high DKH at a PH of 6.8.GH & temp play massive roles in this.
No one can tell you exactly how to achieve this because everybody water is different.
Just test different things & see what works best.
Mr Damage wrote:
I've never heard of the 4 degree KH rule.

I've read that before.It's usually the aquarium lot that say that."Ideal DH (DKH) = 4 & DH (DGH) = 8".One drop or degree = 17.8 ppm of CaCO3

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PostPosted: Dec 7th, '19, 02:55 
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OK, so I just read this a bit closer and while my first answer is valid it doesn't answer the question so I'll give it another shot. I'm just going to throw out some ideas that might help.

misterJOSHUA wrote:
I feel like the 4 degree kh and 6.5-7 ph rule in aquaponics is somewhat impossible seeing how as soon as you add any type of carbonate to the water for the 4 degrees you're supposed to have - the pH inevitably rises to a minimum of 7.2.


It has been mentioned before but it's not a rule. Yes, increasing the KH generally increases the pH so it is difficult to adjust one without the other changing. I generally adjust the pH and not the KH. I use the crushed coral and potassium bicarbonate combination I mentioned earlier - both of these provide carbonates keep things where I want. Of course in my system the pH is always falling so I'm using these to slow the pH decline or to bring the pH back up to where I want it. I suspect most people run a KH around 3 or lower if they have a pH below 7 but I could be wrong :dontknow: .

After adjusting your top up water, instead of just letting it sit, try aerating it before you test it and see what the pH winds up being. This will remove any excess CO2 and would then raise the pH (most likely to be an issue with well water and possibly why your pH goes back up once it's added to the system). Hmm, I see that RO water absorbs CO2 and goes from 7.0 to 5.5 when it's exposed to air - not like normal water :think:. RO water has virtually nothing in it, are you adding back any raw water to it or just using it as is? This test probably won't tell you anything useful if you're using RO water.

While I suspect the ascorbic acid amounts are small and will have little or no affect on the bacteria in your filtration, ascorbic acid is an antimicrobial agent. Hydrochloric acid (aka muriatic acid) works well as an alternative but can be hazardous to work with so make sure you know what you're doing. You may have been harming the biofilter enough that the bacteria haven't been driving the pH down. Seems possible but unlikely.

My recommendation - I would not be trying to adjust he KH. Don't use straight RO water, mix back in some raw water or you'll probably get some problems over time with nutrient deficiencies and other issues. If you aren't feeding much then there is no nitrogen source to drive nitrification that causes the pH to go down. One more thing to consider is that if there are anoxic areas in your grow beds or filters the bacteria will be doing a different process other than nitrification and the pH will get pushed up instead of down. Finally once nitrification kicks in your pH and your KH will fall - This is OK, just start using the CaCO3 and potassium bicarbonate to keep things where you want. FYI there are other ways to do this so you may see CaOH and KOH coupled with a carbonate source as well.


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