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Old 11-29-2007, 02:49 AM   #1 (permalink)
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Default Once more about soft vs. hard water and Ca:Mg ratios

There were many talks over soft/hard water issues so it may seem another one is unnecessary. However, over the

past few months i carried out some experiments on the subject to "uncover the truth". Before i set up my first

planted tank i was often told that one must use soft water. Obviously the word "soft" may be somewhatconfusing:

for some folks it may be GH = 6, for other it may be GH = 3.
So, my first tank was filled with water of GH = 6..7. The water was prepared by mixing some RO water with tap

one. I didn't know what levels of Ca & Mg were in the tank. I used commercial micro and macro ferts. Most

commercial macro ferts usually have very low nitrogen concentrations. By using this macro fert i obtained very

low NO3 and PO4 levels - usually below 5 ppm (sometimes it was unmeasurable). PO4 was typically 0.1 ppm. Under

such conditions the results were as follows:

Case 1.

- most plants grew well (Glossostigma, Umbrosum, Alternatara, Polysperma)
- such species as Cabomba were stunted due to low NO3 (they love high NO3)
- GDA appeared on the glass very often
- BBA grew on many stem plants, driftwood, heaters and on the rear glass
- heavy BGA algae outbreaks occured a few times
- no stunted tips
- rich plants colors
- poor pearling

Three months after setting up my first tank i was advised to use only RO water
reconstituted by a commercial mixture very similar to that of Seachem "Equilibrium". It was the only change i

made (macro dosage wasn't altered - i used the same doses of K, PO4 and N which was in the form of NH4). The

tests showed GH = 2, KH = 1. (laboratory tests were made showing Ca = 8, Mg = 4). PO4 and NO3 were low again

(0.1, 3 ppm respectively). The results were as follows:

Case 2.

- very good and fast plants growth, massive prunings were required every week
- cabombas vere still stunted
- no stunted tips but some Rotala Indica tips were "bald" due to low Ca
- GDA appeared only when there were unmeasurable PO4 and low K doses (no more than 1 ppm a day)
- BBA slowly dissapeared
- rich plants colors
- hard water-loving Cryptocoryne species rot and died
- moderate pearling

Then i got to know about EI method. I added KNO3 and KH2PO4. NO3 rose to 10..15 ppm, PO4 to 1 ppm. Such levels in

very soft water (GH = 2) i had caused the following:

Case 3.

- exceptionally good growth of Cabomba and Blyxa Japonica (Cabomba had to be pruned twice a week)
- a bit faster growth of Didiplis Diandra
- almost all growing tips on Rotalas, Umbrosum, polysperma were stunted
- alternateras had horribly deformed and bent leaves, some specimens just died quickly
- leaves colors not affected by higher NO3
- very heavy pearling
- some plants didn't show any changes in growth and coloration; these inlcuded Glossistigma, Anubias

As you may have read in my previous threads and posts the next steps i made was struggling with stunted tips and leaves deformations; finally it turned out that the issues were caused by low K and high NO3 (and sometimes low Mg) (i always thought it was due to low Ca but adding high amounts of Ca (50 ppm) didn't help at all). However, a few weeks ago i switched to what i've described in Case 2: low GH (it is 3 this time...), very low NO3, very low PO4, high K. Now myt plants show quite good growth, no stunting, no deformations, no problems with algae. It also seems that when using very soft water it should also be low in chlorides, sulphates and sodium - i get the impression they contribute to stunting when they are present in high concentrations. Approximately Cl is below 2 ppm, Na below 5, SO4 comes from MgSO4 and it is about 16 ppm.

Ca:Mg ratio Considerations

It is often said what Ca:Mg ratio we should keep in our tanks. Most sources say about 3:1..4:1.
It seems most of us (if it's possible) attempt to maintain 4:1 ratio thinking it's the best solution to many problems (especially connected with Ca deficiency issues). I can truly say that Ca:Mg which should be kept depends on a few things. When i first discovered that most of my issues with stunting were caused by inadequate K doses i tried to keep K high (usually 30 ppm). It usuallly worked fine for about 2 months but after this time i noticed that many young new leaves became pale and growth was poor. Most plants looked as if they were iron starved so i added high iron doses ending up with over 0.5 ppm Fe in the water column. Such high level of Fe didn't improve anything. I also increased maganese dosage (Mn deficiency may resemble Fe deficiency in some cases) but it was all in vain. Finally i added Mg (Mg was increased from 5 to 10 ppm). In three days i noticed faster growth and pale colors dissapeared within a week. The Ca:Mg ratio at which the improvement was noticed was 2:1.
Such a ratio may induce Ca deficiency (some people on the forum experienced that after adding more Mg) but it seems to me it happens mainly in hard water. When i had 2:1 ratio the only plant that was affected was Cardamine Lyrata. Its leaves were curled upward which was a clear sign of Mg excess but the plant got used to 2:1 radio within a month and the curling declined. In turn, in soft water (GH 2..3) which i use now 2:1 ratio works very well; i don't experience any problems with Ca deficiency or Mg excess. Another thing worth mentioning is what Mg deficiency looks like in aquatic environment. Most articles and literature connected with terrestial plants say, Mg defficiency appears as yellowing on lower leaves. I can say that in many cases it's not true in planted tanks. As i have written above i experienced Mg deficiency that appeared as yellowing on young leaves.
It's often confused with Fe deficiency. If you see something like this, and if you dose high levels of Fe it may be a clear sign that Mg is deficient (unless your current Ca:Mg ratio is 2:1 - in this case pale colors on young leaves may be a result of micro overfertizing). Also, it's not always true K excess causes Mg deficiency. Currently i dose only 4 ppm of Mg to changed water every week and add 2 ppm of K every day and i can't see any signs of Mg deficiency (this routine has been repeated for over a month now)

To Summarize:

1. If you use hard tap water you can dose higher NO3, PO4
2. If you have soft water dose little NO3 and PO4; in many cases with very soft water no NO3 dosing is needed
3. Don't be afraid of high K - in all cases it should be high (20..30 ppm or more)
4. Avoid using fertilizers high in boron; i noticed it's the most toxic element causing slow growth and chlorosis
(however, in some cases high boron levels work fine but i don't know why it happens)
5. Don't be fooled by some Amano tanks where he uses extremely soft water ( for example, GH = 1). I think his tanks have Power Sand substrate enriched with CaCO3.
6. I suppose high N may be used in soft water tanks but only when it's injected under the roots.
7. Hard water is a paradise for snails - you will have to remove 50 or more snails from your tank
every day (unless you use a chemical agent to kill them once and for all but it will also can destroy your plants)

p.s. sorry for such long text... but i believe the hobby requires me to share my experiences (even though T.Barr or T.Amano would deny everything...)
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