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r/PlantedTank•
TestAndLearn

Liquid fertilizer dosing: directly in water column vs injecting in soil

Ferts

Hi Algae growers :)

I recently found that dosing liquid fertilizers in the aquarium soil using a syringe is far more effective than adding in the water column (as per manufacturers' recommendation) for my tanks. Doing this, plants grew lusher and faster, algae buildup was also significantly less.

Is this common knowledge? have people tried this type of experiment before? if so please share your exp

Background and how I stumbled on this-

My 1.5-year-old, 35 gallons heavily planted tank (high tech with 15 neon, 7 otto, and 50+ shrimps) was showing stagnated plant growth despite loading it with co2, Seachem Flourish, Iron, and Trace as per the recommended dosage.

2 months back, I thought my aqua-soil was giving up. Since I could not find root tabs in the market, I just injected a mixture of Flourish (20ml), Iron(5ml) and Trace (5ml) deep in aqua-soil at random spots instead of adding it directly in the water column.

Since I loaded far more fertilizer than usual, I was afraid that algae might take over everything. But to my surprise, plants started growing like a newly planted tank and whatever algae I had before this disappeared. My epified plants (anubias petite and gold) were also doing well.

I am injecting 5ml of this mixture in the soil every week in my 35g. Since last month I also started doing the same for a 5-gallon low-tech betta tank. both tanks had outstanding results.
Unfortunately, since I was really not expecting much out of this, I didn't take before and after photos. But since the actual results are outstanding, I am thinking of doing a properly controlled experiment next. Please kindly share your findings/pointers If you have already done this type of experiment before.

Thanks,

bit thumbs-up for typos

Posted Jan 7, 2022, 12:58 PM UTC

77
KettaiX•

How are you injecting the fertilizer into the soil? This intrigues me.

5
TestAndLearnOP•

Loaded it in 20ml syringe/injection which had a long needle (think its about 10cm needle), it was easy to get from the pharmacy.

1
dusterfreak•

Interesting idea, but I’d imagine you’ve just been pretty nutrient deficient and the big 20ml dose of Flourish has helped counteract it. I’d bet this was caused by your plants getting bigger, the depletion of any nutrients that were in your aquasoil, and inadequate introduction of additional nutrients. Plants need more nutrients as they get bigger, the nutrients in aquasoil deplete over time and don’t replenish themselves, and Flourish isn’t a great fertilizer (in the way you’re using it).

Flourish Comprehensive (contrary to the name) isn’t really designed to provide adequate amounts of nutrients. Especially in heavily planted tanks.

Here’s a quote from SeaChem’s webpage for Flourish Comp.

“Flourish® is designed to be used in conjunction with other macro and micro-nutrient supplements. Other manufacturers try to include ALL necessary nutrients, leading to overdoses of micro-nutrients in an attempt to raise macro-nutrient levels.”

It’s designed to be used as a baseline and supplemented by dosing additional amounts of whatever nutrients your tank is lacking. I use Flourish and supplement NPK, iron and occasionally a few other micros with dry ferts.

Another example, Flourish contains a solution of .07% Nitrogen while AquariumCoop’s EasyGreen has 2.66% and NilocG’s Thrive has 2.56%. Flourish is .01% Phosphate and EasyGreen is .46%, etc. And Flourish is dosed at 1ml per 12gals while EasyGreen is dosed at 1ml per 10gals. So you’re using about as much Flourish and you would EasyGreen (actually a little less Flourish) and Flourish contains less nutrients.

This isn’t meant to plug EasyGreen or Thrive, although they are good fertilizers. Just using the all-in-one fertilizers I’ve seen most highly recommended to give you an idea of what all-in-one fertilizer nutrient composition should look like.

Trace and Iron will help combat this, but you’ll still be pretty short, especially on macros, like Nitrogen, Phosphorus, and Potassium. Nitrogen may be fine due to your stocking (should check by testing nitrates, less than 5ppm in heavily planted would imply nitrogen deficiency) but low Phosphorus and/or Potassium levels seems most likely to have been causing the stall in plant growth.

Trace and Iron don’t add macros. So the P & K levels of Trace, EasyGreen, and Thrive are as follows;

Thrive - P = 1.58% K = 9.7%

EasyGreen - P = .46% K = 9.21%

Flourish - P = .01% K = .37%

So Flourish is providing around 2% as much Potassium and 4% as much Phosphorus as EasyGreen.

You may also have micronutrient deficiencies, but I’m not gonna comb through the data sheets for every single micro like I did with Potassium and Phosphorus. I’d advise you to do it though. Add the percentages of an individual micronutrient from Flourish and Trace together, then compare that number to the percentage of the same nutrient in a reputable all-in-one fert like EasyGreen or Thrive. Rinse and repeat for all the individual micros. Anything in Flourish that’s significantly lower than in the all-in-one fert you’re using for comparison may be a candidate for deficiency.

And I’d imagine the algae was caused by the stall in plant growth. Algae will grow with very little and very high amounts of nutrients while plants need much more than algae. If there’s not enough nutrients, plants deemphasize growth and prioritize retaining nutrients and not dying, then algae outcompetes the plants and flourishes using the small amount of nutrients that wasn’t enough for the plants but is fine for algae. If there’s lots of nutrients, plants outcompete the algae. This is shown in tanks using EI fertilizer dosing. Nutrients are dosed in excess, but, because plants are actively growing, there is no significant algae.

But, again, this is an interesting idea. I’d somewhat doubt the efficacy, because water flows through the substrate, and anything you dose in the substrate will eventually end up in the water column and vice versa. But a more concentrated, direct dose may help absorbent clay substrates suck up more nutrients than they would from a more diluted dose in the water column. Probably depends on how long it would take a substrate dose to dilute into the water column.

5
TestAndLearnOP•

Thank you, this is super helpful,

I have been relying on Seachem products for many years and had/have built up lot of inertia to try other products, I will try EasyGreen and Thrive for sure in the future.

What you said is right, it's a 1.5-year-old high-tech tank, I think soil had lost most of its fertility, I originally wanted to get root tabs but couldn't get them soon enough hence tried this.
From what I have observed, under soil water circulation drops in aged tanks, I also have full carpet to add to the problem. Since most plants take nutrients first from the soil, my theory is that 'the water column fertilization becomes less effective, i think this is also why so many people recommend using root tabs in addition to normal fertilization for aged tanks.

From this experiment, I am concluding that I don't need root tabs or even water column fertilization. just putting liquid ferts in soil is doing a good job. Not sure it will apply to other tanks but definitely will be doing a control experiment soon :)

2
dusterfreak•

Sure thing. I’ve heard great stuff about Thrive and used EasyGreen myself with great results. Maybe look into dry fertilizer too, if you have the time. I use NilocG’s EI Dosing pack. Lot more cost effective and allows you to dose individual nutrients or adjust the amounts of them. Using them is more complicated than all-in-ones and took me a while to wrap my head around. Check out EI dosing or PPS Pro if you’re interested.

SeaChem makes some great stuff too. I use Flourish and Prime myself and am a big fan of both. Flourish’s problem is that it’s sort of marketed in a way that makes you think it’s a comprehensive all-in-one fertilizer, and effective on it’s own. When it usually isn’t.

I’d still say that most of the improvement you’re seeing is due to the larger dose of fertilizer, and you’d see a similar improvement dosing a large amount into the water column.

I agree that substrate circulation will vary depending on the type of substrate, how much it’s compacted, plant coverage, and current strength. And it’s never going to have as much circulation as the water column. But unless you’re getting major pockets of gasses from anaerobic bacteria in the substrate, there’s decent circulation and a liquid fert won’t remain there for more than a day or two. Like you said, your Anubias benefited from the 20ml dose too. Meaning that the fertilizer made it’s way from the substrate to the water column and provided nutrients for the Anubias. And if someone used root tabs in a tank with very little substrate circulation, nutrients would get trapped in the substrate and accumulate, eventually burning the roots and harming the plant.

Root tabs are effective because they’re a solid object that easily remains under the substrate long term and slowly releases large, steady amounts of nutrients. These nutrients will also make their way into the water column, but any nutrients that leave the substrate are constantly being replaced by the tab.

Dosing liquid ferts under the substrate may be more beneficial than nothing, more-so with a nutrient absorbent substrate. But not comparable to something like root tabs, imo.

Regardless, dosing that way won’t really hurt anything. I’d just recommend that you not assume injecting liquid ferts into the substrate will be able to take the place of root tabs without at least trying them out first.

1
ping8888•

great idea.

must find a long syringe, breeders tanks aren't fun to work with sometimes :D

3
TestAndLearnOP•

the syringe was actually easy to find, most pharmacies keep 10cm needles. if it's difficult in your area i would recommend looking for a pharmacy that holds pet supplies or is near veterinary clinics

1