PO4 Dosing Frequency - The Planted Tank Forum
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post #1 of 35 (permalink) Old 08-18-2018, 01:01 AM Thread Starter
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PO4 Dosing Frequency

I’ve been wondering, recently, about my approach to PO4 front-end (weekly) dosing. Searching around, I found these comments by T Barr:
Quote:
K+ , Mg, Ca are more like plain old salt in terms of use by plants. They can be fairly high and left there.
Further on, he states:
Quote:
plants have sets of enzymes for each concentration of NO3, CO2, and PO4.............(low, med, high, very high etc), keeping them within a decent range allows you to keep the plants growing at a nice stable rate.
This seems to imply that if we front-load, as the PO4 is consumed day after day, it will be more difficult for the plants to adjust to the need to vary their enzymatic activity.

Then he goes on to say:
Quote:
Plants will adapt and pull in as much N/P as they can, but they require less energy to do so at higher concentrations. This gives us the highest rate of growth
which seems to contradict his previous contention …or does it?

I know some of you prefer to dose throughout the week. For those that do this because they believe it better than weekly, have you tested it doing it every other day, then doing it weekly, then doing it every other day again to affirm your beliefs?

More broadly, does anyone have any studies that support more regular dosing of PO4 than weekly?

I’m asking the community to convince me that it is better to dose PO4 more frequently (on days other than FE dosing) than once a week.
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post #2 of 35 (permalink) Old 08-18-2018, 03:12 AM
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Point 2 is saying its best to maintain a stable concentration for NO3, PO4 and CO2

Point 3 is saying higher concentrations require less energy to get.

So to me, these two do not contradict.

Ive never tried completely front end loading, ie one big dose per week, but some folks seem to be having good success with it.

I do dose macros with the intention of keeping the same levels in the water at all times, without getting too anal about it.

My NO3 is 25 ppm per week. I dose 15 after the water change and two more 5 ppm doses through the week, as you would with a normal EI routine.

The big dose is to get the level back up to a baseline, and the two smaller doses are theoretically replacing what the plants use throughout the week. Doing it this way avoids having a big drop in concentration the first few days of the week that you get from 3 equal doses.

Is it better? Idk, plants seem to like it better but I havent tested the methods side by side to see if it really makes any difference. But it definitely maintains a more even concentration.

As for dosing Fe and PO4 on the same day, I dont see an issue. This dance takes place according to the totals in the water column. It makes little to zero difference if they are added at the same time, imo. PPS folks have been doing it for years.
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post #3 of 35 (permalink) Old 08-18-2018, 04:05 AM Thread Starter
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Quote:
Originally Posted by burr740 View Post
Point 2 is saying its best to maintain a stable concentration for NO3, PO4 and CO2

Point 3 is saying higher concentrations require less energy to get.

So to me, these two do not contradict. .
Agreed and, the two points combined, implies the need to dose to maintain throughout the week, as you currently do. I dose up to 8-10ppm PO4 after the w/c and, by weeks’ end, it’s down to 4ppm. Not stable, but not sure it matters at that ppm level.

Quote:
Originally Posted by burr740 View Post
As for dosing Fe and PO4 on the same day, I dont see an issue. This dance takes place according to the totals in the water column. It makes little to zero difference if they are added at the same time, imo. PPS folks have been doing it for years.
Yup, I probably shouldn’t have put this distraction in. With my worst level being 4ppm, and dosing FE daily, I’ve never seen an issue (haze or FE deficiency). However, I’m adding .3ppm FE daily and it’s DTPA so, it wouldn’t show quickly at any rate.
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post #4 of 35 (permalink) Old 08-18-2018, 04:12 AM
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Deanna I love your style … this is gonna explode.

“K, Mg and Ca can be high and left there”.
K and Ca yes, but not Mg. Higher Mg reacts with K and Ca uptake and can easily make plants unhappy. You have a garden, pour some MgSO4 out there and watch some plants turn yellow in an hour.

There is this believe that if more food is forced into plants, better they are. Well, maybe with geese in limited time but not with plants or people. It can actually be detrimental. See luxury uptake.

Some are preloading 5 - 15 ppm PO4 and on top add 3 x a week 2 - 5 ppm PO4 when saturated plants can take only 0.1 - 0.2 ppm PO4 a day, hmmm.

Yes, plants will adapt and take as much N and P as they can, but it is up to us not to poison them with excess. Plants are greedy leading to their own destruction. Over fertilization burn is common.

You are asking about weekly versus daily dosing. Low to medium light will do with weekly dosing, but high light works better with daily dosing, tested and nothing new.

Quote:
Originally Posted by Deanna View Post
More broadly, does anyone have any studies that support more regular dosing of PO4 than weekly?
First, you don’t believe in studies and second, plants can uptake PO4 in minutes so it makes sense to dose more often.
Quote:
Originally Posted by Deanna View Post
I’m asking the community to convince me that it is better to dose PO4 more frequently (on days other than FE dosing) than once a week.
Of course it is better unless there is plenty and the “on days other than FE dosing” is non sense since the beginning.
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post #5 of 35 (permalink) Old 08-18-2018, 06:27 AM
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Originally Posted by Deanna View Post
This seems to imply that if we front-load, as the PO4 is consumed day after day, it will be more difficult for the plants to adjust to the need to vary their enzymatic activity.
@Greggz did some interesting calculations in his journal that showed how front-loading can actually keep the levels more consistent throughout the week than multiple doses during the week. He made some assumptions when trying to account for daily plant uptake combined with what his fish were producing, but if I remember correctly, his weekly testing showed his assumptions to be largely accurate.
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post #6 of 35 (permalink) Old 08-18-2018, 12:40 PM
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Quote:
Originally Posted by burr740 View Post
I do dose macros with the intention of keeping the same levels in the water at all times, without getting too anal about it.

My NO3 is 25 ppm per week. I dose 15 after the water change and two more 5 ppm doses through the week, as you would with a normal EI routine.

The big dose is to get the level back up to a baseline, and the two smaller doses are theoretically replacing what the plants use throughout the week. Doing it this way avoids having a big drop in concentration the first few days of the week that you get from 3 equal doses.

Is it better? Idk, plants seem to like it better but I havent tested the methods side by side to see if it really makes any difference. But it definitely maintains a more even concentration.
As we discussed some time ago, with normal EI dosing the ppm concentrations gradually build up throughout the week. The water change brings the levels way down, then they slowly rise and peak right before the next water change.

So the idea here was to get a more stable level of ferts throughout the week. Front end loading keeps mine stable because I have a large fish load. So between the natural creation of N & P and plant uptake, my levels stay very stable all week.

With a lower fish load (or lower plant mass), you would do as you are doing, and use one larger dose after water change, then smaller doses throughout the week. But even if you front end loaded everything, it would just be kind of the opposite of the EI system. Instead of getting a build up and peaking before a water change, you would peak after a water change then be at lowest levels at the end of the week.

Now does it really change anything? Who knows? My tank is better than ever, but that could be for a multitude of different reasons as well. Like I have said, from a pure convenience factor, I will keep with it.

And keep in mind this depends on what theories you subscribe to. For my tank, I keep everything well above non limiting nutrients. Others have more success with very low levels of nutrients. To each his own and there are plenty of ways to manage your planted tank. It's figuring out which one produces the best results in YOUR tank that's important.
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post #7 of 35 (permalink) Old 08-18-2018, 02:19 PM
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Originally Posted by Greggz View Post
My tank is better than ever, but that could be for a multitude of different reasons as well. Like I have said, from a pure convenience factor, I will keep with it.
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post #8 of 35 (permalink) Old 08-18-2018, 02:50 PM Thread Starter
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Three different experiences (which I’ve known existed) already that will probably set the pattern for what may come in further posts. For now, I’ll add a few comments based upon each point that strikes me. I may skip some points to avoid creating a treatise.

I do plan to maintain high range 8-10ppm initial PO4, just to inhibit GSA, but continue to wonder what beneficial stability might mean in a high tech tank. Is it keeping +/- 2ppm (via dosing throughout the week) or is dropping by 4-5ppm (from a weekly dose) by weeks end harmless? In some areas (NO3) I am gravitating toward the PPS approach, but believe that my too-great fish load will limit me in other areas.

Thanks for the input. I’m probably going to try maintaining a stable +/- PO4 level, breaking with my weekly dosing of that nutrient, since uptake of that clearly is something I can counter. NO3 uptake does not keep up with fish organics, so I will continue not adding any N for now.

@Edward first:

Quote:
Originally Posted by Edward View Post
Deanna I love your style … this is gonna explode.

“K, Mg and Ca can be high and left there”.
K and Ca yes, but not Mg.

Some are preloading 5 - 15 ppm PO4 and on top add 3 x a week 2 - 5 ppm PO4 when saturated plants can take only 0.1 - 0.2 ppm PO4 a day, hmmm.

You are asking about weekly versus daily dosing. Low to medium light will do with weekly dosing, but high light works better with daily dosing, tested and nothing new.

First, you don’t believe in studies
It’s a little scary that you have a fairly good read of me. You’re right: I am highly skeptical of studies thrown about to support one position vs. another. I think there are severe credulity issues that are created from the Internet. Such studies usually send me out looking for corroborating experiences from people I develop a trust in. So far in this post, that includes everyone that has posted. You mentioned that you’ve tested the daily vs. weekly issue in high tech situations. Did you document that process in any of your postings or website that I can take a look through?

I’m taking Barrs’ comment “K, Mg and Ca can be high and left there” not to mean deadly high, but just that weekly dosing works for these three, the word “high” being relative. I believe that there are upper limits to all of these before they become detrimental. I’ve seen comments and studies (uh-oh) regarding Luxury Uptake dangers, but view these as no different from any potential toxicities …stored or not. I am guilty of front-loading PO4 in your assigned high range, but it is purely to inhibit GSA which, I’ve found, it does. I haven’t seen any reports that high levels (5-15ppm) of PO4 either are toxic or inhibit uptake of other nutrients. I know I can burn my lawn with too much N or P and have come to believe that NO3 is better for plants in the 5-10ppm area in my tank (used to be happy with 20-40ppm).

My NO3 now starts the week at ~5ppm and builds to about 10ppm by weeks’ end. As mentioned, PO4 starts high and ends low. No dosing of either after the initial PO4 dose. Although my interest in this thread was about PO4 stability, I’m wondering if my plants are growing better at the beginning of the week or at the end of the week and does the varying PO4 and NO3 level impact this? Rhetorical question and possibly unknowable.

Quote:
Originally Posted by Greggz View Post
So the idea here was to get a more stable level of ferts throughout the week. Front end loading keeps mine stable because I have a large fish load. So between the natural creation of N & P and plant uptake, my levels stay very stable all week.

And keep in mind this depends on what theories you subscribe to. For my tank, I keep everything well above non limiting nutrients. Others have more success with very low levels of nutrients. To each his own and there are plenty of ways to manage your planted tank. It's figuring out which one produces the best results in YOUR tank that's important.
This is, exactly, the conclusion I came to in my overly-crowded and high biomass tank. Also agree with the uniqueness of individual tanks that, I believe, is the butterfly effect that we create by our individual approaches. I do think that we curve-fit our additives/water params (CO2, ferts, minerals and substrate) based upon certain critical aspects such as 1) quality and intensity of light, 2) fauna load and food, and 3) plant types and quantity. If you had @Edwards identical setup of these three criteria, I believe that his additives approach would give you the same results as he gets and that he could match your tanks’ performance if reversed.

I abandoned pure EI some time ago, but with an eye toward maintaining non-limiting supplies. I do think that, for a high tech tank, beginners should follow EI. I now gravitate more toward @Edwards lower thresholds for N, which seems, to me, to be the best flywheel to use to maximize – or throttle – growth while maintaining full health, but I do push PO4 well above EI and micros at the higher levels you and @burr740 do.

I’ve been front-loading everything but micros for years, but am now questioning if it is actually creating significant detrimental instability, mainly the PO4 (for now), although I may end up playing with N if I move the PO4 and see positive changes. Thing is, I’m happy with my tank, but always wonder if there is just a little more that I might squeeze out of it.
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post #9 of 35 (permalink) Old 08-18-2018, 03:29 PM
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Edward I agree with you. This fall/winter I plan to address this, and try some different dosing regimens with otherwise the same set up.

Of course, won't really prove anything, but should be good food for thought. More to come.
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post #10 of 35 (permalink) Old 08-18-2018, 03:36 PM Thread Starter
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Edward I agree with you. This fall/winter I plan to address this, and try some different dosing regimens with otherwise the same set up.

Of course, won't really prove anything, but should be good food for thought. More to come.
Oooh! What are in your plans?
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post #11 of 35 (permalink) Old 08-18-2018, 04:55 PM
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Edward I agree with you. This fall/winter I plan to address this, and try some different dosing regimens with otherwise the same set up.

Of course, won't really prove anything, but should be good food for thought. More to come.
Say what!!! So the real questions are 1- will you be duplicating existing plant selection or expanding? And 2- what kind of rainbows? Going with the smaller species this time??
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post #12 of 35 (permalink) Old 08-18-2018, 05:23 PM
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We must not stop reminding Greggz this is plantedtank-forum not rainbowfish-forum.
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post #13 of 35 (permalink) Old 08-18-2018, 05:29 PM
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We must not stop reminding Greggz this is plantedtank-forum not rainbowfish-forum.
Wait, you mean it's not plantedrainbowtank. Com? ... perhaps a revolution is coming? :-)
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post #14 of 35 (permalink) Old 08-18-2018, 05:47 PM Thread Starter
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I thought it might be turning into a shrimp forum, despite @Greggz best efforts to show us the gold at the end of the Rainbows. However, I do note in his post, above, that he is, in fact, referring to fert changes.
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post #15 of 35 (permalink) Old 08-18-2018, 06:02 PM
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I thought it might be turning into a shrimp forum, despite @Greggz best efforts to show us the gold at the end of the Rainbows. However, I do note in his post, above, that he is, in fact, referring to fert changes.
Ha yeah I did read that, but had to take the opportunity. I'll refrain from digressing any further!
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