trilinearmipmap

Thanks for an interesting thread, Kekon.

I wonder if you can help me with my macronutrient dosing.

I have a 75 gallon tank, CO2 injected to 30 ppm, 220 watts of cf lighting.

My tap water is very soft, 9 ppm total dissolved solids which is about 1/2 a degree of hardness so I am using virtually RO water out of my tap. I am doing the EI method and have had problems with poor growth and algae.

My dosing with each weekly 50% water change is as follows:

CaCO3: 3 tsp
CaCl2: 2 tsp
MgSO4*7H2O: 3 tsp
K2SO4: 2 tsp
KH2PO4: 1/8 tsp
KNO3: 1/4 tsp

With feedings my nitrates are around 20 so I am looking at eliminating the KNO3 dosing and increasing water changes to bring nitrates down to around 5. I'll also try eliminating the CaCl2 as you have suggested.

My question is, do my amounts of CaCO3, MgSO4 and K2SO4 seem about right or should I change them?

puttyman70

Sorry that was supposed to be all N's. Basically right now I'm dosing Seachem's full line per this spreadsheet.

http://www.aquaticplantcentral.com/f...tor-chart.html

Its a 29 gallon tank with 4.5 w/g, pressurized c02, gravel substrate with root tabs, soft water 2dkh and 2dgh. I am getting reading of 0 nitrates and phosphate with lamott's test kits. If I am dosing these and still getting 0 I assume I need to up the dosages but how do I figure out how. I am sure you can tell me but I would like to understand the math and relevant formulas so I can do it myself eventually.

Thanks very much for your help. Maybe a text book?

kekon

I'll try to reply puttyman70 and trilinearmipmap in one post (sorry for inconvenience)

puttyman70:

If you still read 0 ppm NO3 and PO4 i recommend to simply double the doses. Also, i think it would be wise to add Seachem Nitrogen after water change. As far as i know Seachem Nitrogen adds little nitrogen in one single dose; that's why you read so low NO3 and PO4. Because you have very soft water you don't need to dose as much N as it is needed to reach "recommended levels" such as 5..10 ppm NO3 or 0.1..0.5 ppm PO4 etc. So i think you should double the doses and wait several days untill NO3 becomes detectable by your test kit (it seems to me 1..3 ppm NO3 will be enough). In the past i also had GH = 2 and very low NO3 (about 2..3 ppm) and PO4 0.1 ppm and the tank was doing pretty well (except 2..3 plant species). If it turns out you still read undetectable NO3 and PO4 despite higher doses it will be a good thing to add KNO3 and KH2PO4 (i realize Seachem fertilizers are not cheap and dosing more and more can become quite expensive).
When it comes to potassium i think Seachem Potassium recommended doses are quite enugh (if you want to use your own compounds such as K2SO4 or KHCO3 you can add these weekly in dry form)

As regards math, it's not difficult. Let's take old and good KNO3 and KH2PO4 (all the commercial fertilizers are made of them)

KNO3 contains 61.3% of NO3 and 38.7% of K.
1 ppm = 1mg/l.
29 gallons = 3.785 * 29 = 110 liters.
So if you want to add 1 ppm NO3 into your 29g tank for example, you should dose 0.18 grams of KNO3:
0.18 grams of KNO3 contains 0.18 * 61.3% = 0.11 grams NO3. 0.11 grams NO3 / 110 liters = 1 ppm NO3. (0.18 grams of KNO3 added to 29g tank will raise NO3 of 1 ppm and K of 0.63 ppm)

Because 0.18 gram KNO3 is very low amount and it's difficult to measure using teaspons it's better to make KNO3 solution in RO or distilled water. Simply dissolve 22.4 grams of KNO3 in 250 ml disstilled or RO water (22.4 grams KNO3 = 4 tsp). 1ml of the solution will add 0.5 ppm NO3 in your 29g tank. You can add such dose daily; 0.5 ppm NO3 daily will be enough in you tank with very low GH.

The same routine you can apply to KH2PO4. I think it would be enough to add about 0.1 ppm PO4 daily in your tank. KH2PO4 contains 69.8% PO4 and 28.7% K (here, K can be neglected)
To make PO4 solution dissolve 2.5 grams of KH2PO4 in 250 ml of water (2.5 grams of KH2PO4 = 1/2 tsp). 1ml of the solution will add 0.06 ppm PO4 in 110g tank (dose 2ml daily so you will be adding 0.12 ppm PO4 each day)

If you wish to add potassium in a form of K2SO4 dose 1/2 tsp weekly (after every water change).
K2SO4 contains 44.9% of K so adding 1/2 tsp = 2.5 grams will add 10 ppm of K (this amount will be enough in your tank). You can also use KHCO3. In this case 1/2 tsp will be adequate as well.

Hints:

1. When making solutions put dry salt into empty bottle first and fill with water up to desired volume.
2. The lower GH the less NO3 and PO4 (this will not apply to many plant species but some stem plants are sensitive to higher NO3 in very soft water)


trilinearmipmap:

I calculated you add the folllowing (approximately):

10 ppm Mg
70 ppm Ca (45 ppm from CaCO3 and 24 from CaCl2)
43 ppm K
42 ppm Cl

In my opinion there is too much Ca and Cl and you may experience Mg deficiency. You can use only CaCO3 as a source of Ca because the amount you use adds enough Ca (45 ppm) so CaCl2 can be wholly eliminated. It seems to me that high level of Cl (as a result of using CaCl2) may be harmful to some species. CaCl2 can be used but in smaller amounts (so as not to add more than 20..30 ppm Cl)
As regards NO3, you have to add less KNO3 so as to reach no more than 10 ppm (i know i was telling about 5 ppm but due to low accuracy of test kits they can lie and in fact it could be less than 5)
I see you add quite high K amounts. This doesn't cause leaves deformations, twisting etc. but can contribute to Mg deficiency. I also added 40 ppm K to changed water in my tank routinely for 3 weeks but it made my plants very pale (it looks like Fe deficiency but it is not). So i recommend to use halt that dose of K2SO4 you add. If you experience such paleness on you plants also increasing Mg could be very helpful. To summarize, i think you should do the following:

1. Stop using CaCl2 but use CaCO3 (the same amount you add currently)
2. Add some more Mg (3.5..4 tsp)
3. Add 1 tsp K2SO4 instead of 2 tsp
4. Try to lower NO3

You have to perform this routine for at least 1..2 weeks to see the improvement.

CaCO3 is difficult to dissolve but it's solubility can be greatly increased by grinding it into dust by means of a mortar. It's clunky however, but it makes CaCO3 dissolve much faster (in a matter of hours). Some people dissolve CaCO3 in HCl acid but it's very bad because the reaction will produce CaCl2 which we want to eliminate.

trilinearmipmap

Thanks for the advice.

I will try your dosing routine for 4 weeks and watch the results.

My CaCO3 is "CaCO3 light", it is a very fine powder, it forms a cloud in the tank when first dosed but it all dissolves within one hour.