Fertilizer Recommendations & Info - the Informal FAQ

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AC Members
Mar 25, 2003
Los Angeles, CA
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Plant maintenance and fertilizers can seem truly daunting at first. I was certainly overwhelmed when I first discovered all of this. but thanks to the insight and kindness of the people here at AC, I've been able to get a better understanding of it all, and I want to share this with the AC community.

So, in an attempt to collect and consolidate information regarding fertilzers, I have searched this forum and pasted some good snippets below. This is not written in stone. If corrections or additions need to be made, please do so. But maybe we should keep this like an FAQ (read: minimal OT discussion :p ) for AC members to refer to when they are wondering what fertilizers to use .

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

For Traces - use Flourish - 10mls 2x week
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"

What AC members have said:

to put it simply, aquatic plants require the following:

1. quality and bright lighting.
2. proper substrate with high cation ability and root fertilizer
3. carbon dioxide gases
4. liquid trace elements

in general, if you purchase good quality flourescent lights (for eg. Arcadia brand, 1-2W/gallon) meant for tropical freshwater tanks, use a 3-inch depth of 1-2mm sized gravel substrate mixed with flourite (plant growing substrate), add fertilizer tablets into the substrate and add liquid fertilizer in small amounts daily (during a fish feeding time), most plants would be able to do well.

however as pointed out by Oriongirl, if you want a real overgrowth of plants in the tank, CO2 will be essential as its effects are very obvious within a short period of time. as CO2 units are expensive, DIY sources or an increase in the number of fishes in the tank may also help.

Macros are Nitrogen, Phosphate, and Potassium or N, P, K. They are the macronutrients as opposed to the micronutrients (Iron and other minerals). I use Flourish and Flourish Iron for micros, (am about to try some Flourish tabs because I feel like I space on micros too often). I use Spectracide Stump Remover to supplement Nitrate, NuSalt for Potassium, and Fleet Enema for Phosphate (just a few drops).

Tropica Mastergrow for the water.
Aquarium Pharm Root Tabs w/iron and Jobes Fern & Palm spikes for the gravel.
Fourish Excel for carbon usable by plants in the water.
Flourish Iron in water every other week esp with red or heavily planted tanks.

Liquids are best dosed daily in smaller amounts than weekly in larger doses. Gravel ferts should be added at least every 3 months.

gnome: (in the same thread as above)
I was too embarrassed to buy a FLEET . It was just my luck that the last time I decided to buy a couple of items from ThatPetPlace, I happened to find that they carried Flourish Phosphorus. I think it must be a fairly new product in the Flourish line. They had Flourish Nitrogen, as well. I know they've had Flourish Potassium for a while...

I like that it has dosing directions. I'd think there would be a greater tendency to overdose with FLEET, and aside from my being self-conscious about buying it, I would have been concerned about adding too much. With a large enough tank, however, there's more room for error and the FLEET might be an economical option.

I agree that Tropica Master Grow is a good product for traces, but right now I'm trying to finish an endless bottle of Flourish. For macros, I use stump remover (KNO3) and sulphate of potash (K2SO4). I've also found that for some plants, the Jobe's fertilizer spikes do wonders - just make sure you use sparingly and bury the pieces very deep. I also dose with Flourish Iron and as I mentioned already, Flourish Phosphorus. And I have noticed that my plants that are planted in Flourite are much more robust than those growing in sand or coarse gravel.

anonapersona: (in the same thread as above)
Basically, rooted plants may do fine with substrate fertilizers, but the sticks that many use are bad about creating algae if they are disturbed. If you have stem plants or plants that are on rocks or wood, like java fern and the like, you'll probably need fertilizers in the water column.

You can't go wrong with the Seachem line, or so I hear from those that use it. I was pleased with the Dupla24 drops that I used daily, though they ran out pretty quickly.

The reason that everyone keeps directing you to the home-made fertilizers is that you will go broke trying to fertilize the big tank. For example, Nutrafin Plant Gro iron enriched was about $8 at the Local Fish Store. 5 ml/10 gallons or 50 ml/100 gallon tank.... replace the bottle after 4 3/4 doses. They do not mention how often that might be but let's assume weekly. So, $8/month.

On the other hand, for $11 including shipping, I got a few years worth of traces, and for a year or more's worth of KNO3 was $2 at the feed store. For $7 I got 40 lbs of KCl which I am using up at about 1.5 grams per month so this will last me about 1000 years. I don't do phosphate yet, but I know I can get the Fleet stuff for $1 on sale at Walgreens from time to time.

plantbrain – Tom Barr:
Trace= the flourish, this will help. Add 5mls 2x aweek.
Flourish potassium: Add enough to get 20ppm once a week.

Do 50% weekly water changes. Call tap water company, see what the PO4 is or if they add polyphosphates to their/your supply. If so, that will take care of the PO4 needs of the plants.

K2SO4 is cheaper than Flourish K+/potassium. 5$ worth would last 10 years, maybe more for all the K+ needs.
KNO3 can be added if the levels dips down below 5ppm. About the same cost as the K2SO4.

For some more info:

You'll spend much less time measuring and guessing if you do a simple routine.


If you want to dose K, why not pick up some K2SO4 or KCl which can be bought at your supermarket either with the salt products or in the dietary dept under the name 'NoSalt' or 'NuSalt'
K2SO4(Potassium Sulfate) is cheaper than KCl, but a little tougher to find. Can be bought on-line here: www.litemanu.com
Go to 'Shop on line' - Nutrients - Chemicals and scroll down to Potassium Sulfate.

Re: Crushed Coral: If you go to LFS and ask, they will probably give you a couple of cups full of crushed coral that they use in their salt water tanks. Most stores usually have some laying around. Put 1/2 tbsp. in a small nylon bag and put it into your filter. It will help raise your kH and you won't have to mess with it after that unless you want the kH higher(add another 1/4tbsp).

Flourish Excel is a decent source of carbon for moderately lit tanks, tanks with low pH and very little kH(as it doesn't cause pH crashes)..and for tanks on the small/med size range. The cost of flourish excel would make it expensive to use on large tanks, and it isn't nearly as good as using CO2 injection for high light tanks. I use it as a DIY CO2 supplement on my tanks..mainly on my 10 gallon that has 3wpg of lighting that I can't seem to achieve high enough CO2 levels with the DIY CO2 and HOB filter.

Root tabs are great for swords, crypts, anubias, and other "rooted" type plants..especially when first added to a "virgin" substrate. They aren't absolutely necessary, however, in mature flourite/onyx sand containing substrates with a good amount of fish mulm present within. I no longer use root tabs in my substrates for this very reason. However, if I purchase a "new" rooted-plant, I might add a root tab near it's base to help it get established.
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Fish?.......What Fish?
Aug 19, 2002
Somerdale, New Jersey USA
Don't Forget Salt Petre

Excellent Job Nanahachi,
I would only include Salt Petre as an alternative for KNO3.
And I'm told that the Flourish Root Tabs for "ponds" are exactly the same ingredients as the regular Flourish Root Tabs, and you get twice as many tablets in the box.
This should definitely be a Sticky. It's like an instant reference for the new-comers who ask the usual beginner questions.

Here are two more products that are 100% KNO3 and can be used for dosing N:
Green Light Stump Remover
Grant's Stump Remover - this one is a bit more difficult to measure as it comes in pellet form rather than a fine powder.
Available at Ace Hardware and OSH.

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NJ Devils Fan

#1 Devils fan
Oct 28, 2002
Yonkers, NY
A while ago when I asked what fertilizers to get, someone told me that all flourish excel was was just watered down flourish. The problem I had was that I was getting a lot of black algae on my plants, it was beating the plants to the nutrients. The CO2 wasn't enough. So, I got Flourish, flourish Potassium, and flourish Phosphate, all made by Seachem. I took all the algae out by hand whatever I could get, and I've been adding my fertilizers 2x a week and I have been making sure my DiY CO2 is flowing ok. I have not seen any algae since, and that was over 2 months ago. If algae grows on plants, it usually means that something is not ballanced. You could have too much light and not enough CO2 or visa-versa. In my case, I did not have enough nutrients in the water, and what little nutrients that were there, the algae was beating the plants too it.

EDIT: spelling
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AC Members
Mar 25, 2003
great post, but be cautios with your quantites. I saw Plantbrains recommendation of 5ML of FLourish a day. That would be for a 125-150 gallon tank, 2ML a day for a 55 gallon tank.

this link is a quick calculator of how much dry powder to mix to get your tank where you want it (as well as recommendations for target quantities for each nutrient)

Potassium Nitrate is a fireworks chemical, available all over the place (skylighter.com) and is a good source of Nitrate. Let's use that to calculate the dose using the link above.

First fill in the gallons for your tank size, then the quantity of solution you want to mix up (250 or 500 ML are best). This is how much water you will want ot have in the container to mix the powder into. I personally mix 250 ML of solution with 8 teaspoons and then add 50ML of the solution a day. Each ML will increase my tank concentration by .23 ppm, 4ML adds almost 1 ppm of nitrate. I like to try to keep my nitrates around 15.

Now, as for chemicals, I get all mine from Off-ice.


Dec 9, 2003
Halifax, NS
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Great post, one comment, both KNO3 (for nitrate) and KH2PO4 (for phosphate) also contain potassium (K). I haven't actually calculated the doses, but I'm guessing that they alone would provide sufficient K.
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AC Members
Feb 27, 2004
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A question for clarification on the following:

"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."

I looked in my local stores in the UK and couldn't find this brand. All the brands that I found are 50% KCL and 50% NaCL - can these be used or does it have to be 100% NaCL? Havent managed to find K2SO4 anywhere.


Dec 9, 2003
Halifax, NS
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From a strictly chemical standpoint, there's nothing wrong with it per se, except you'd need to double the doseage. From a fish/plant physiology standpoint, I'm not sure. I wouldn't think that the quantities suggested, even when doubled, would be sufficient to affect any plants/fish sensitive to salt. But then, maybe some people more experienced in fish keeping could answer that. Perhaps this discussion should be it's own thread, not in the sticky.


AC Members
May 23, 1999
Manila, Philippines
hi how about using fertilizers not meant for aquarium plants?
like growmore orchid fertilizer meant for orchids?

30-10-10 formula?
i'm planning on experimenting on my anubias plants...
do you guys this this could work?


Dec 9, 2003
Halifax, NS
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No. As you've noticed we try to keep NO3 around 10 and PO4 around 1, that's a 10:1 ratio. The Orchid ferts have a 3:1 ratio, in other words, you'd end up with abour 3 times the PO4 you'd need. I think that it's a recipe for disaster, i.e. algae.

As a rule, using ferts for terrestrial plants, i.e. what you'll find at home depot, will be a)too strong or b)mixed in the wrong ratio. Plus, you'll likely find that as your tank evolves, you'll need to change the amount of N or P or K or traces that your tank receives, so premixed ferts aren't a good call, IMO. Get the individuals as recomended in the thread and mix your own using Chuck Gadd's aquarium calculator.