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Re: Seachem Prime

Kirk M. responded to my request for more info on his tank:

75 gallons, 130 watts CF lighting, 40 watts fluorescent lighting,

Interesting. I guess I would consider this moderate light -- roughly equivalent to 3W/gal NO on the whole.

30% water change 1x per week, CO2 injection - 1 bubble per 3 seconds,
KH = 8 dKH
GH = 5 dGH
pH = 7.0-7.2

CO2 looks ok.

Nitrate = approximately 8 ppm

Surprising. I was expecting less.

Nitrite = 0
Ammonia = 0
I have no idea about iron or potassium - don't own a test for it.

I have an Fe kit, but I rarely use it. In fact, I haven't touched it in a year or more. I don't think a person really needs either test kit.


I base this on having approximately 60 gallons of water in the tank with the substrate.

Seachem Flourish (1 mL, 2x per week)
Flourish Trace (approx. 15 mL, 2x per week)

You might want to boost the Flourish dose, but that can wait until you get the current problem figured out.

Flourish Nitrogen (approx. 3 mL, 2x per week)

Using the "expert" formula on the label, and using your tank volume approximation of 60gal, that would be the equivalent of 1 / ((0.05 * 60) / 3) = 1ppm NO3 each dose. So, you're adding the equivalent of 2ppm nitrate each week. That's doubtfully enough and also doesn't seem to jibe well with the 8ppm you mentioned above. Some discrepancy can be attributed to testing error and the estimation of water volume, but a 6ppm gap seems wider than those things can account for. Do you have nitrate in your tap water or big/numerous fish (i.e., lots of nitrification)? Does the nitrate level go down from day to day or does it seem to be building up?

Flourish Potassium (approx. 6 mL, 2x per week)

That's not much at all (~2ppm per week), and since you're using Flourish N rather than KNO3, you won't be getting much extra. I add about 10ppm K once a week to supplement the amount that comes from the KNO3 I add. The total K added is around 20ppm, maybe a bit less in my moderate light tanks. Excess potassium doesn't 'cause' algae or, within reason, harm livestock, but K is critical in regard to the plants, so it's prudent to keep a healthy supply in the water. In other words, overdosing K within reason is preferable to underdosing.

Low potassium may help explain the problem you're having, too. Plants will only grow as much as the least available nutrient allows. You definitely don't want K to be that limiting nutrient, which may be the case. Try increasing the amount of K you add and observe how the nitrate level behaves (and plants, too!).

I use K2SO4 for potassium by the way. I like Seachem's product, but it can get pricey when running large or multiple tanks. Ditto on Fe, but I haven't yet gotten around to replacing that.

Flourish Iron (approx 6 mL, 1x per week)

In my experience, it's better to spread Fe dosing out across the week, at least when using Seachem -- it doesn't seem to last very long in the water column. I add extra Fe before the lights come on each day between doses of Flourish.

Flourish Tabs, at roots of swords 1 time per 2 months, or Jobes, whatever I have at the time.

Careful with those Jobes. The first time you dig one up may send you on an algae adventure.

Photoperiod is 12 hours.

That'll work. -- Chuck Huffine Knoxville, Tennessee