Co2, Fertilization, Algae and more updated 10/10

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John N.

AC Members
Feb 1, 2006
Co2, Fertilization and more

Estimative Index Fertilization Method

Let’s cut to the chase. People want to have a lush planted aquarium with as little work and money as possible. When it comes to fertilizing the aquarium finding an easy, cost-efficient way can be quite a predicament – but it doesn’t have to be.

The Estimative Index (EI) popularized by Tom Barr is a straightforward fertilization method for dosing nutrients in a planted aquarium without the need for monitoring water parameters. This method works on the basic principle of supplying more nutrients to plants then what they actually consume during a week’s timeframe. At the end of each week, the hobbyist “resets” the aquarium and nutrient levels by performing a large waterchange that flushes out the system. This whole process creates an “estimative” amount of nutrient levels that are more than adequate for plants to grow healthily.

The Estimative Index method works best with high light and heavily planted aquariums, but can work with lower light levels and less plant mass by reducing the frequency or amount doses in the suggested regimes. It assumes the aquarium will have adequate CO2 of 30 ppm or above. In both high light and low light situations, the hobbyist will dose fertilizers daily according the instructions below, and do a weekly 50% water change.

The primary fertilizers used in any planted aquarium are the macro nutrients – Nitrogen (N), Phosphorous (P), Potassium (K), and the micro/trace elements (Plantex CSM+B, Seachem Flourish, Tropica Plant Nutrition). Iron (Fe) can also be supplemented if desired, but in most cases not necessary.

How do I use these fertilizers and the Estimative Index?

Fertilizing via EI is simple. Every other day dose the prescribed macros elements, and on the off days add in the trace/micro elements. Perform a 50% waterchange at the end of the week. By following one of the commonly used dosing programs below for your specific tank size you can ensure your plants are getting what the need throughout the week.

10-20 Gallons
1/8 tsp KNO3 3x a week
1/32 tsp KH2PO4 3x a week
1/32 tsp K2SO4 3x a week
1/32 tsp (2ml) traces 3x a week

20-40 Gallons
1/4 tsp KNO3 3x a week
1/16 tsp KH2PO4 3x a week
1/16 tsp K2SO4 3x a week
1/16 tsp (5ml) traces 3x a week

40-60 Gallons
1/2 tsp KNO3 3x a week
1/8 tsp KH2PO4 3x a week
1/8 tsp K2SO4 3x a week
1/8 tsp (10 ml) traces 3x a week

60-80 Gallons
3/4 tsp KNO3 3x a week
3/16 tsp KH2PO4 3x a week
1/4 tsp K2SO4 3x a week
1/4 tsp (15ml) traces 3x a week

100-125 Gallons
1 1/2 tsp KNO3 3x a week
1/2 tsp KH2PO4 3x a week
1/2 tsp K2SO4 3x a week
1/2 tsp (30ml) traces 3x a week

Example of a dosing program for a 29 gallon tank.

*K2SO4 is not required for dosing unless you need the extra Potassium (K). This K is found in KN03 and KH2P04. Dosing these two according to above will yield sufficient K levels. Therefore, one will be fine dosing only KN03 and KH2P04, and Plantex. However, if one finds the need to supplement the K2SO4, there is no harm by dosing this chemical as part of your fertilization regime.

Where can I buy the fertilizers and chemicals? can provide you with the necessary chemicals for dry and liquid dosing of the above. For micro - trace elements, Plantex CSM+B, Seachem Flourish, and Tropica Plant Nutrition are equivalent to each other. For the Seachem and Tropica brands visit and

One pound bags of each of Aquarium Fertilizer Chemicals will last at least 1 year:

· (Trace) Plantex CSM+B
· (N) Potassium Nitrate KN03
· (P) Monopotassium Phosphate KH2P04
· (K) Potassium Sulphate K2S04 (optional)

Special Notes:

Providing optimal CO2 levels of at least 30 ppm are necessary for plants to prosper and out-compete algae. If algae issue arise, remove all visible algae and infected leaves. Recheck CO2 levels, and possibly reduce and adjust the lighting period.

Direct dry dosing into the tank is perfectly fine. Many dosing straight into the tank, or they dissolve each chemical in water before adding.

Making a Liquid Stock of Plantex CSM+B is more often mixed into a bulk liquid solution since some find it more convenient to dose their trace elements this way. The recipe for this solution is 1 tablespoon to 250ml water is equivalent to: 20 ml = 1/4 teaspoon of dry Plantex. This solution is stored in refrigerators to prevent mold from forming within the container. For making stock solutions for NPK use Chuck Gladd's Conversion Calculator.

Small dosing teaspoons (smidgen, dash, pinch) can be found at Linen & Things, Bed Bath and Beyond, Wal-Mart, dollar stores, eBay and other online retailers. To identify the specific measurements of your smidgen, dash, pinch set, a 1/8 tsp should fill a ¼ tsp in 2 tries, 1/16 tsp in 4 tries, and a 1/32 tsp in 8 tries.

You will see results right after the first week of dosing. Your plants will grow faster and your plants will look healthier. Keep with the dosing program, and you'll see your planted aquarium become a nice looking showpiece for your home.

-John N.
Last edited by a moderator:

Staff member
Jun 4, 2003
Co2, Fertilization and more

Another EI article which goes into a little more detail if you wish to knwo
Estimative Index Fertilization Method

PPS Perpetual Preservation System

Walstad method

CO2 and light stimulate the growth

DIY Root Tabs

DIY Ferts

A Nutrient Calculator

target levels

Nitrates 10-20ppm
Phosphates 1.0-2.0 ppm
Iron 0.1-1.0 ppm
Potassium 10-20 ppm

Absolute Must Haves - Traces & Macros (N, P, K)

For Traces - use Flourish - 10mls 2x week or Plantex CSM+B
For Nitrate (N) - use (KNO3), such as Spectracide Stump Remover, Salt Petre, Green Light Stump Remover, Grant's Stump Remover
For Phosphate (P) - use Fleet Enema (KH2PO4) - 3 or 4 drops after water change. Test at mid week and if under .5ppm dose again to reach 1.0ppm.
For Potassium (K) - use No-Salt / Nu-Salt (KCL) - 1/4 tsp. per 20 gals. after water change. Or you can mix a stock solution and keep in the refrigerator. Mix 1tbsp. K2SO4 with tap water in a 300ml bottle. Shake WELL until dissolved and dose 10ml 2x week in a tank of 30 gal. and over and 1x week in a tank smaller than 30 gal.

Should Haves - Micronutrients
For Magnesium - use Epsom Salt
For Iron - use Flourish Iron - 5mls per 20 gals. 2x week
For Carbon - use Flourish Excel &/or CO2 injection (DIY or pressurized)
To increase KH (Carbonate Hardness) - Baking Soda or Crushed Coral
Nutrients for plant roots – Jobes (fern & palm) or Flourish "Root tabs"
Another place to get dry ferts is from Rex Grigg Best Aquarium Regulator And Bobs Tropical Plants

Using KNO3 as the sole source of K+(no K2SO4/KCl needed by Tom Barr


ada soil seems to be the best but costly. its hard to find local but you can order it online. one thing with ada soil is it kicks off some nasty ammonia spikes. i would soak it and water change for a month before i used it. it also has peat in it that lowers the water ph.

Mineralized Top Soil
Its more of a diy substrate though some people do sell kits on planted tank forum and APC. how to guide can be found here.

eco complete / Flourite / Flourite sand all three about equal some like one over the other. make sure to wash the gravel more so with flourite.

soilmaster select / Turface this stuff is a very cheap option $11-20 for 50 pounds. its clay based with a high carbon exchange capacity. it is dusty and takes a long time to clean even after cleaning you can still see some dust when moving around. it does suck up KH and in turn lower your ph. soilmaster select and turface have been discontinued in charcoal (black) but there are other clay based options out there.

3m colorquartz ok this is inert not really a plant substrate per say but if you can find it at about $25 for 50 pounds its cheap looks great and can be mixed in with your other substrate. now discontinued but there are other quartz products out there.

Shultz Aquatic Plant Soil never used it my self but you should clean it like any others.

layering is another option. another thing i never used but i feel its best for more advanced users.

Substrate Calculator
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Staff member
Jun 4, 2003

co2 is often the most limiting factor in planted tanks. some plants need it and can speed up plant growth by 10 folds.

there are 3 common ways to add carbon to your planted tank. pressurized co2 diy co2 or excel which is a liquid form of carbon. excel can melt some plants and the gas is a better option if you can afford it.

for a pressurized system there will be more up front costs but cheaper in the long run.
must have: co2 tank, regulator, needle valve and a way to break up the co2
optional: Solenoid, check valve, ph controller, drop checker

tips on pressurized co2 set up.

co2 buy as big as you can fit. i have a 20 and a 10 pounder. the bigger ones only cost a few more to refill and last longer.
regulator there are many different ones out there. rex grigg makes top of the line one and will help you with every step. many people also pick up Milwaukee regulators on ebay or other sites.
needle valve lowers the psi so your out putting 1-2 bubbles per section. each take is different so it might take time to dial in what yours needs.
solenoid isnt a must but lets you save co2 by shutting it off and on at night or hooked up to a ph controller.
check valve keeps water from backing up for what ever reason and flooding the house.
ph controller with a ph controller you can set it for the ph you want. once it gets to that level it will shut the co2 off.
drop checker this is a simple yet great way to measure co2 in you tank visually. it changes color as the co2 levels raise or lowers. one important part is to make sure you have 4kdh liquid to fill it with.

Drop Checkers/CO2 Indicators-Why and How

the problem i often see is how to break up the co2 into the water. there are lots of options.... glass diffuser input or output of a filter, reactor, ladders, power heads, wood air stones and more. all these have their own place some work better then others. ill break them down with pros and cons in how i see them. again my experience might be different the others.

Glass diffusers breaks up the co2 into small micro bubbles great to put under the out put of the filter to help blow them around. the con is it can clog up over time.
input/output filters one of my more favorite ways to break up co2. i put the tube into the input or to the out put of a canister filter or hob. this breaks it down really well and spread though out the tank. the con in the input it can air lock a filter some claim it even breaks down a canister. con for the output doesnt always break up the co2 as well as input
reactor is a great diy type of way to break co2 up. i feel the best ones are working with the output of a canister powering it. there are also intake reactors but take up tank space.
powerheads are another one of my favorite ways to break up co2. it does take up some take space but it breaks the co2 very good and pushes it though out the tank.
wood airstones while these work they dont work very well

tips on DIY co2
its very easy but takes time. you need soda bottle/juice bottle sugar yeast tubing.

mix 2 cups sugar and 1/2 tsp of yeast with warm water 2/3 the way high. it should last 2 weeks or so depending on temp. i would also highly recommend adding a 2nd smaller bubble counter. this will keep the mixture out of your tank.

Co2 Thread

i say its only good up to 20 gals tanks though people do use multiple bottles.

a couple places to get regulators that i have seen here.

Best Aquarium Regulator

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Staff member
Jun 4, 2003

lighting is a major concern. its what every plant needs to grow. there are many options and you can go on for days reading about light. i will try and make this very simple. often people add too much light get frustrated and quit. if your starting out i suggest starting off with a low light tank. get the basic down before moving on to a higher light high tech set up.

one thing to remember about lighting is making sure you get the right bulb. some are better then others. i tend to stay in the 6500k - 10000k bulbs. many fixtures that are sold comes with Actinic bulbs. these do not help much for plants. you will just end up replacing them. often if you look you can find the freshwater set ups.

T5/T5HO is the most efficient lighting source that all the plant people are using. individual reflectors can give a great boost of light into the tank but they dont all come with them.

Fishneedit Cheap T5 fixtures

compact fluorescent (CF) runs hotter then T5 another great option. lights are wonderful and many people use only them. others will work and are fine.

Ahsupply good place for CF retrofit kits and t5 retrofikt kits.

Compact fluorescent lamp (CFL) it might take work but make sure you get the daylight 6500k bulbs. these are good options on 20 gal or under tanks though they can be used on bigger tanks. they are not very efficient but do work.

T8 is slighting better then t12 shop lights. they can be found at any hardware store. again look for the daylight bulbs. i find they work the best. there are "plant bulbs" but often they give off very unattractive coloring. one great thing about these is you can over drive them. over driving doubles up the power going to the bulb and gives about 50% more out put.

T12 common shop lights can work though i like t8 better.

Metal Halide (MH)
not used by the majority they run hot and not to efficient mostly used on large planted tanks. They Do allow you to get a lot of light over a area.

LED The future is LED lighting. the bulbs last practically forever. They use a lot less energry and give out more light for the energy used. However as of now they are mostly on high end systems or are put together by hobbyists.
Designing and Making a LED Light Fixture for a Planted Tank
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Apocalypse Pony
Apr 16, 2008
So Cal
Real Name
Co2, Fertilization, Algae and more updated 6/08

This guide is for everyone that asks about DIY tabs, since I could never find a real good guide through google, so with the help of Jake from, I present my process and ingredient list. Enjoy

I use equal parts Red Pottery Clay and Plantex CSM+B, but you can tailor it further if you need more macros in the tank or have very little water hardness, etc.

You can add Potassium sulfate, Magnesium sulfate (epsom salt), Potassium nitrate or Calcium nitrate, etc. You can't add any phosphorus because it will precipitate with the iron in the Plantex and clay, as the clay is iron rich naturally.

The typical mix:
3/4 cup plantex csm+b
3/4 cup red pottery clay
2 tablespoons potassium sulfate
2 tablespoons epsom salt
2 teaspoons potassium nitrate.

If it were going in a well-stocked tank, I'd leave off the nitrate.

The trick to it is to add only as much water as you need. I use distilled water, but reverse osmosis filtered water would be fine as well. I use a syringe to gradually add the water, as it takes less than you'd think to mix it to the right consistency. You want to only add enough water, and add it gradually enough, until you can mix and mold the stuff and it's not sticking to anything.

I roll it into small little balls and sit it on some tin foil or wax paper to dry. I usually leave it to dry a couple of weeks or so. I do not bake them, and from talking with others, the results arent very good, they get fragile and crumbly after that.

From there I'd just use it like any other fertilizer tablet. They dissolve quicker than you'd expect, but they last long enough to get them in the substrate. From there it doesn't really matter because it's all trapped under the substrate. You don't want to hold one under water while you think about where to put it, but you have enough time to get it from your hand to where you want it in the substrate before it dissolves.

Hopefully this helps, especially with the cost of root tabs, and if you already have all the dry ferts, then the clay is the only real setback.

If anyone has question, post them here or shoot me a PM, thx.


AC Members
Apr 27, 2001
Davis, CA
The other helpful thing I think that's often overlooked with algae and what is really growing plants well(algae is more a symptom of a plant issue), is the light.

I can grow most plants better, easier, with less electrical cost, initial expenditure and with less chance of nutrient , Co2 or algae issues using less light, in general, 2w/gal will meet most anyone's demands if you use CO2.

Many buy CO2 and then think they now must add more and more light.
You are adding to CO2 to increase the health and growth, as well as now being able to grow many different species without them competing with one another for CO2.

You get 5-20X more growth even with lower light by adding CO2 gas.
Careful with what you wish for, it's not just light that amplifies growth, and adding more light means more CO2 demand and more nutrient demand. So the balance will be harder as you add more and more light, the corollary is you have an easier time with nutrients, algae and CO2 with less light.

Plants grow well, moderate rates, no algae to speak of, easier to tweak nutrients/CO2, fewer water changes etc with less light.

If you double the wattage on a 55 gallon tank from 2-4w/gal, you waste about 50-60$ a year on electric alone. At a high rate of water cost, doing the same 50% weekly water change even at a high rate of water, cost you 5-6$ per year, not much..........and the water change be used to water house plants, the landscape outside etc.

It is best to have light as the limiting factor for growth of the plants, this is much more stable parameter than CO2/nutrients. Which in turn makes algae control much much easier, your system will have far better resiliency and stability over time.

Since demand is lower for CO2, less is required and less stress is placed on fish with CO2. Also, if you forget to dose, less of an issue, or if you want to run the nutrients leaner, not a problem with less light, or if you want to use more % from the sediment(Say mineralized soil or ADA aqua soil etc), this is a wiser.........also.

Some like the idea of using the fish load for most of the nutrients and then dose lean, this also works well in conjunction with a nutrient rich sediment like the ADA AS or MS. However, adding more does no harm's just not needed however, better to run a bit rich and not limit those and have light as the limitation factor for growth.

So you have far more wiggle room using this approach with less light.
Also, when you go away for vacation for a week or two, lower light tanks always do much better and have less issues.

Common sense stuff, but hobbyists often get lost in the details and do not stand back and look at the big picture. So the plants grow 20-30% slower with less light, you gain 90% easier time caring for them. Patience is a virtue and rewards those using less light.

Tom Barr
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