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New Member
5 Apr 2008
Gentlemen, please forgive me if this subject has already been raised, however I can find no mention of it after exhaustive searching. After a lapse of 40 years, since I last attempted to grow Cryptocoryne in the very limited technology of those days, I have maintained a tank using modern principles, including EI, and injected CO2 with some success. Recently a VERY old friend invited me round for a drink, and after some time discovered that he too maintained a plant tank. When I first saw this, I was frankly speechless with admiration, the plants, and especially the Cryptocoryne, were magnificent, huge stands that I have only ever seen in books. He runs a Dennerle system, with injected Co2, and a Deponit substrate, and originally used Dennerle ferts, however he became fed up with the cost of these, and shifted to EI.One day he had no Ei available and decided to try using Phostrogen, he has no fish just plants, and on the basis of what has happened since, has continued to use it with seemingly astounding results. He doses, and I have seen him do this, 'about a quarter teaspoon evey other day', and changes 'about 30/40% of the water every other week. Please Gentlemen, I have read Tom Barr's erudite writings over and over again, and those contained in this site, how is this possible?, I note that most of the Nitrogen in Phostrogen is from Urea and not Ammonium, but is he nurturing a ticking timebomb?, or is my name justified?


New Member
Thread starter
5 Apr 2008
James, Thank you Sir for the reply, I will read the relevant link thoroughly, and perhaps will do my own experiments with Phostrogen, could be interesting. Far too late now, but how I wish I had read Chemistry instead of Physics....much more interesting now!


2 Aug 2007
There is also no fish...........

Then you can dose it, also, as with time.........the bacteria bulld up and take up any that the plants do not get and use.
Also, with lower ranges of light and good CO2, the impact of urea/NH4 will be reduced.

NH4 seems to induce GW only for the most part, I suspect after dosing NH4 for a time, at least at rates under 0.8ppm per day, the bacteria will build up and keep the residual at zero ppm.

If you suddenly dose NH4, or overload the system with too many fish(and more than say 0.8ppm a day of NH4), then you get algae, GW first, followed by reds and finally greens.

But the rate of NH4 coming in is a key part.
NH4 is toxic and far more volatile than NO3, which even at a very wide range, cannot induce algae.

NH4 is a lot more touchy than NO3.

I think as far plants go....adding fish adds all the NH4 you ever might need.
Much easier and much nicer to look at. Crypts are pretty easy plants to grow and require low light, so it's not surprising really.

BTW, most all my aquariums have lots of fish, much more than ADA's tanks.

But then again, I like fish and started keeping fish before plants.
Like most aquarist.

I think the algae issue is more open and less centered around NH4 than perhaps I felt in the past, but if you overload a system, dose makes the poison.

Since bacteria plays a role in transformations NH4=> NO3, that has to be considered also when a regular dosign at small amounts etc is done. Just like slowly adding more fish when stocking an aquarium, it is no different than that.

As long as the plants keep the NH4 low and stable, there's no issue.
Lower light also keeps the algae from blooming, and reduces CO2 demand from plants.

I think algae might listen to NH4 loading rate and wait for high spikes, and similarly, do a similar thing with CO2 changes. We can vary these two over a wide range(not merely just dosing low amounts) and induce algae pretty consistently.

If CO2 is stable and stays that way, plants seem to adapt well.
Same for NH4 as long as the plants can remove it and/or the bacteria can also transform it into NO3.

If not, then we seem to get algae.

I can only discuss a certain set under which algae is induced, but things like CO2/light need addressed also, and the ppm's of NH4, not merely whether you add some or not.

Tom Barr


Expert/Global Moderator
Staff member
11 Jul 2007
Chicago, USA
Yep, there are plenty of garden mixes that will work, even the stuff from Tesco. These are all the same basic ingredients and as with any ammonium based product you can get bitten if you go over the top. As Tom says, if there are no fish and if the lighting isn't outrageous you have a much greater margin of error.

The Phostrogen Lawn Food product is listed on the datasheet as NPK 38-5-5, the contents of which are 11% Potassium Nitrate (KNO3) and 9% Ammonium Dihydrogen Phosphate NH4H2PO4 so it's very high in Nitrogen as well as being very soluble.

Ammonium has a much higher concentration of Nitrogen than does Potassium Nitrate.
KNO3 is only about 14% by weight of N while NH4 is nearly 78% by weight of N. If they're using Ammonium Nitrate then this is 35% by weight so there is a lot more bang for buck from an N standpoint so of course Urea/Ammonium based products will have a higher yield and will be cheaper to produce.