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What nutrients do plants actually require?


3 Jul 2007
Bexley, Kent
Been thinking about this recently from another thread where someone decided that tap water was full of 'nasties' and shouldn't be used to reconstitute reverse osmosis (RO) water. I've always added tap water to my RO water as I believe that tap water contains lots of 'goodies' that are required for healthy plant growth.

If RO water is reconstituted with GH booster or something like Seachem's Equilibrium and you dose Estimative Index via dry powders or dose Tropica TPN+, then you'll have the following in your water:

CO2 (carbon)
NO3, NH4 (nitrogen)
PO4 (phosphorus)
SO4 (sulphur)
Sodium (if you add baking soda or KH up products)

Am I correct in believing that other elements are also beneficial to the plants? These are some I've found whilst doing a quick search:

Chloride (chlorine)

It is possible that some or all of these are present in fish food and the substrate, but I don't know. I notice that some of the Seachem products contain these elements - Trace Comparisons - so possibly they are beneficial. But I would also bet that good old tap water contains everything as well.

The only nasties I can think of in water are chlorine and chloromines. Also possibly some heavy metals. All of these can be made safe by using a decent water conditioner. But are the heavy metals at any concentration to be concerned at anyway or it is just scare mongering?

Just some thoughts
You might find this interesting James.


Flouride, pesticides, arsenic, radium, copper, lead, murcury, chlorine, chloramine, Trihalomethanes (solvants or refrigerants) , hormones, aswell as nitrates and phosphates. Thats what I meant when I described them as 'nasties'.

I am no chemist nor have I ever pretended to be one. I simply use 100% ro water as it is a totally foolproof method which is 100% safe. In fact chemists (proper ones with phd's employed by manufacturers of reminarelising salts that is) have done all the hard work for me. Therefore I don't need to worry about the simple fact that my knowledge of such things is very limited, just do what it says on the tin.

I am hoping that similar chemists have done their job right when they created the trace element mixture that I use and coupled with the macro nutrients, light, heat and co2, my plants needs are completly met.
One of the problems with websites that are trying to sell you a water filter is that they are naturally going to make your tap water seem like it's toxic.

You have a lot of faith in remineralising agents. For example Seachem Equilibrium contains the following:

Potassium Sulphate
Calcium Sulphate
Magnesium Sulphate
Iron Sulphate
Manganese Sulphate

Most of it is potassium sulphate. There is nothing else in there, especially nothing from the second list of elements that I mentioned above. They may or may not be required, but don't expect to get a complete selection of elements, because you won't. I know when I used just Seachem Equilibrium I had poorer looking plants than when I just used tap water. This may or may not have anything to do with the Equilibrium but one thing I noticed is that with a similar GH and KH the TDS was extremely high with the Equilibrium.

Thing is plants may be happy with just what's in Equilibrium and in the dosing, or they may require more. This is what I'm trying to find out.

Hi James,
Empirical data indicates that tap, unless contaminated with herbicides, have very few negative issues as far as plants are concerned. It's impact on fauna and on humans is a different story. Chloride, for example, although much maligned, is essential for photosynthesis. It's an unbound anion, which means that it does not tie itself up in complex compounds, and acts as sort of a mobile free agent. This is a similar function to K. Because of the many positively charged (cations), mostly metals, chloride, which is negatively charged, is used to balance electrical charges within the cells as well as to control cell turgidity and osmoregulation. Silicon is used by some plants to strengthen cell walls.

Many metals such as copper, nickel and selenium are used in photosynthesis as they pass on charges along the Electron Transport Chain. These are recyclable though and are only used in very small quantities. Many of these exotic metals are interchangeable with other, more commonly dosed metals such as magnesium (depending on the reaction) so their absence may not have a significant effect when using RO. It would be difficult to test the effects of their absence, or to even test for their presence for that matter.

So "contaminants" from our perspective ought not to be confused or correlated with that of plant's requirements.

Plants, aquatic that is, wetland or otherwise, are used precisely for mitigation of both contaiminated water, and sediments.
They have entire books on the topic.

Plants will take up other things, they do not really need, Hg, Se, gold even................organic compounds, they have a host of enzymes to detoxify things. And they just store many chemicals.

Some of the purest water flows through lots of forest and wetlands etc. The Rio Negro has very good water quality. If the rainforest is removed, this will no longer be the case.

It's loaded with tannins, but the quality is still extrmely high.
Where I'm at, we have sierra snow melt and no vegetation, granite mountains and high quality as well, but through a different hydrological process.

The water at the end on the Everglades typically had/has, PO4 levels almost immeasurable at about 3-10ppb.
Plants cannot grow in this water BTW, algae can though and it is about 50% of the production in the Everglades, plants need at least 20-50ppb PO4 to do okay.

Reddy has a lot of research and books on the topic, (UF, an old prof of mine).

Tom Barr
As far SeaChem's EQ, Ca, Mg, SO4, K+, they add a little Fe/Mn as wellm but I dount those have much effect.

So CaSO4/MgSO4/K2SO4, at a 1:1:2 ratio by weight takes care of things for a DIY version if you so choose.
That nails everything else beside the KNO3, KH2PO4 and trace mix.

Tom Barr
I think we are also looking at this issue from different angles James.

The plants seem to me to be your main concern and fair enough if thats where your priorities lie and if the water meets the needs for your fish, but for me my main concern is for the welfare of my soft water delicate fish species first and the plants second.

You are quite right in your assumption that I place a great deal of faith in 100% remineralising ro water. I don't wish to tempt fate when I say this but I never experiance unexplained fish deaths and I do keep some delicate species. Sure the odd one dies of old age sometimes or being bullied but thats about it, I haven't lost a fish in the last two years though.

That is the basis of my faith in using 100% remineralised water and is unlikely to change unless fish start dying for causes which I can't fathom out. I also run UV sterilisers on my tanks and quarentine every new addition for at least a month before adding them to existing stocks.
Healthy plants = healthy fish.

Plants generally will remove more, RO water is fine, but as far as toxicants, activated carbon does most of the issues, RO just removes KH/GH mostly.

Blending is all you likely need to do target a KH, not 100% and then redo the minerals.

Tap water is not toxic, but those bottled water companies, wonky whacky water hucksters selling homeopathic baloney(the new snake oil sales people) should be avoided. If it's got a bit too much of something, say NO3/KH, then an RO can reduce that. Organics or unknowns, typically carbon does the trick in virtually all cases.

If you do not try somethign else, you really cannot say that much about why and how the fish died prior, or why they do well today etc. When I focused on the plants, the fish issues went away. When I started doing large % weekly water changes or more, just like breeders without plants, I also no longer had issues.

Doing both, I have no issues.
Nice thing with carbon is that it's cheap, and no waste water.
Plants remove the other items(NO4/PO4 etc).
KH/Gh is mostly what's left after that. So blending works well for that rather than 100% reconstituation.
I think some rattle on over safety, mostly LFS's selling the RO units etc.
So their motivation for pushing such fears is suspect.

Tom Barr