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Dealing with old growth after switching to proper fert dosin

san-ho-zay

san-ho-zay

Member
Joined
18 Jun 2008
Messages
98
Location
Otley, UK
Hi 🙂

After a few bouts of algae, and largely thanks to great information and links on here, I'm completely sold on the whole idea of proper plant fertilisation.

The tank in question has been set up from about November last year - Rio 300 (standard 2x54W T5 with reflectors). It was all going well for the first few months up to March, then I got various algae outbreaks. I'd added pressurised CO2 the month before but getting to grips with it and having a dodgy drop checker probably meant varying levels. And I was only using Nutrafin Plant Gro if and when I remembered 😳.

Anyway, I'm pleased to say that I seem to have turned a corner. After discovering high phosphates in my tap water (> 5mg/l on a phosphate test kit) and initially jumping to the conclusion that they were the cause of the algae, I've done lots of reading and been dosing Seachem Nitrogen, Seachem Potassium and Waterlife Topiflora religiously for about three weeks. Water changes have been upped to 40% a week. I've also got my drop checker sorted out and been spot-treating odd patches of BBA with Excel. It all seems to be working and I'll be switching to dry powders when the bottles run out (KNO3, K2SO4, GH booster & trace mix). My water is very soft (KH 10-20mg/l and GH 20-40mg/l).

My question is how to deal with the plants that are left. I've been gradually pruning and removing the worst leaves but not cutting right back or replacing. Having read that ammonium is the major algae trigger, I'm wondering if it would be better to just clear out any algae affected growth in one go?

Here's a couple of examples:

H. difformis
Hdifformis.jpg


Blyxa aubertii
Baubertii.jpg


You can see the good growth coming through but the older leaves have some algae left. It's not getting worse, but should I be clearing it out and replanting the new growth?
 
Hi Richard, welcome aboard the good ship UKaps. 😀

Congratulations on taking the plunge and doing your research to boot.

You've done the hard part in getting new growth from struggling plants so don't let them get effected buy the rest of the plant. Take some time and prune as much of the algae covered leaves, trim as close to the root or leaf node. Your plants will repay you by putting all the nutrients into new growth and in no time you'll have no algae at all. Just be sure to have enough plants to absorb all the added CO2 and nutes. Too fewer plants is a massive problem IMO.

Good luck pal.
 
Thanks for that Dan and thanks for the welcome 🙂.

The recommended dose on the Seachem bottles is a lot lower than the dosing I've been reading about in the context of EI. Dosing three times a week gives 3mg/l nitrate per week with the Nitrogen and 6mg/l potassium per week with the Potassium. I've been doubling that this past week on the basis that it's important not to run out of anything.

Once I get the dry ferts, I was going to aim for 10mg/l nitrate and 15mg/l potassium per week, which would be half the maximum uptake rates I've seen quoted for EI dosing schemes with high lighting. Does that sound a reasonable starting point?
 
Thanks for that. I take your point about the phosphate.

This might be a stupid question but something that's puzzling me is that K doesn't seem to be treated the same way as N, P and Mg :? I used a dosage calculator against the reference 20 US gallon to try and understand it better and, if I've done my sums correctly, the NPK and Mg dose for the week is:

Nitrate (NO3) 27 mg/l
Potassium (K) 22 mg/l
Phosphate (PO4) 11 mg/l
Magnesium (Mg) 10 mg/l

In the EI thread it quotes these as maximum uptake:

Nitrate (NO3) 20ppm per week.
Potassium (K) 30ppm per week.
Phosphate (PO4) 3ppm per week
Magnesium (Mg) 10ppm per week

I can see why the phosphate dose is so much higher if we say 1/16 tsp is the minimum realistic measure. But why isn't the potassium dose higher, i.e. why isn't K2SO4 used to get the potassium over 30?
 
Hi Richard,
There is enough K from the KNO3 and the KH2PO4 if dosed per the reference tank or scaled from those numbers on a larger/smaller tank. You can add more K but it doesn't really do much. The Nutricalc still has K2SO4 but it was discovered later that you don't need as much K. I'm not sure which dosing calculator you are using. I'll have to review the molar weights again to verify the numbers.

Cheers,
 
Thanks guys. I note that AE's GH booster has some K2SO4 anyway.

If you are still interested, the calculator I used was http://www.theplantedtank.co.uk/calculator.htm.

In 20 USG ...

KN03 : 3/16tsp (0.1875) : N = 9.11, P = 0, K = 5.75, Mg = 0
KH2PO4 : 1/16 tsp (0.0625) : N = 0, P = 3.8, K = 1.56, Mg = 0
MgSO4 : 1/2 tsp (0.5) : N = 0, P = 0; K = 0, Mg = 3.33

Totals : N = 9.11, P = 3.8, K = 7.31, Mg = 3.33

Multiply by 3 x per week: N = 27.33, P = 11.4, K = 21.93, Mg = 9.99

But it's just academic. I'll shut up and follow the doses 🙂
 
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