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24 Sep 2007
Please bear with me if you've just been answering my questions in the CO2 thread! I've recently traded up to a 180 litre tank and am now slowly (as money permits) upgrading its contents. The lights are in now and I've got a little Nutrafin CO2 on the go - and am plucking up the courage to get a pressurised system on the go.

So now to nutrients... I have to say I'm a bit confused. I know none of you rate test kits too much, but both my nitrates and phosphates are testing high, and yet my plants look as though they are in need of ferts - holes in leaves and that sort of thing.

I'm finding it a bit confusing I suppose - I expected that when I started the CO2 that the nitrates and phospates would drop - or that I'd have a bad algae outbreak, but neither have happened.

I ordered some Plant Nutrition + but haven't dosed for fear of kicking off the algae. What do you think is missing?!

Thanks as always in advance for advice :D
Hi nicky,
One thing is for sure is that I rate NO3/PO4 test kits lower than dolphin manure lying at the bottom of the Atlantic Ocean. It's just not a very good strategy to assess your nutrient requirements based on test kit readings. Sometime the kit readings are accurate and sometimes they are way off. The problem is that you never know which reading is the good one. Unless you calibrate the kit you have absolutely no idea what the actual concentration levels are. The fact that your plants are deficient while your kit tells you everything is fine and dandy is simple proof of their unreliability.

If you throw the kits in the bin and adhere to the dosing principles you will be much further ahead.

If you were dosing dry salts a 180 liter highly lit, CO2 injected tank would get the following:

3X per week 1/2 teaspoon KNO3
3X per week 1/8 teaspoon KH2PO4
3X per week 1 1/4 teaspoon MgSO4

2X per week trace element mix

I can't translate that to TPN+ dosing so I imagine you can dose per bottle instruction. Someone else may have a better feel for the dosing of this product.

In any case, whichever you use, if you dose these values then you know absolutely that your plants will never be deficient, because these values provide more than you need. If you depend on test kit readings you are basically using tarot cards.

In my opinion it's upside down to not dose due to fear of algae. Dosing prevents algae. 8)

If you go by George's dosing of TPN+ then it would be approx 2ml per 100USG per W

i.e. a 180 with 1WPG would be approx 4ml
a 180 with 2WPG approx 8ml