Target Levels - Average or High point?

[scolley]

In my first only tank, I've finally gotten over the fear, and basic learning to do regular fert dosing (NPK CO2 Fe Traces). Thanks everyone for all your help with that!

But I find that I do not understand "targeting". My tank is growing, without much algae, and it rips through a good bit of nitrate and phosphate daily. So every day I measure, and every day I have less than my "target" amount. I dose to bring up to target levels, and can confirm that level thru testing shortly after dosing. But the next day, I'm always a good bit lower than the target level again - repeat this process daily.

So can someone give a bit more definition on the concept of "targeting"?

Does a target mean a high point to shoot for, but not go beyond? I'm doing that now, so my target level will only be held a short time before going below target.

Or does it mean to dose to some point above your target, so that levels will fall back to a point where the target actually represents something like an average level?

Love to get some direction from the community on this. Thanks.

[Wasserpest]

There aren't any fast and hard rules. You will find recommended ranges, like NO3 from 5 to 10 ppm, and in a high-light tank you would target the upper limit of the range, since, like you said, it rips through the nutrients so quickly.

There is no harm for levels to fall below the optimum, as long as they do not zero out for extended times. Aside from higher energy cost, high light equals high maintenance, including possibly daily dosing... that's why I stay away from it!

In any case, I think you have a good understanding of the dosing principles. Target means what you bring up your levels to when dosing, then plants use that and before it bottoms out you dose again.

[scolley]

Thanks Wasserpest. I'm only testing and dosing daily temporarily. I'm trying to get good records on how much the tank goes through. That way, I can not only dose less often, but I'm hoping that I can test less frequently than that, having built up a solid understanding of the tank's requirements.

So your thoughts on "targeting" is that that target is the point you bring it up to, prior to the almost immedate drop again. Got it. Doing that now.

But I think that you may be too kind in thinking I've got a good understanding...

To use nitrates as an example, I have indeed been targeting between 5 and 10 ppm. Knowing that was the standard range, I've been targeting 7.5 (or as close as I can discern with test kits). And maybe that's wrong.

Maybe I should be targeting 10, and managing things so it doesn't fall below 5. I've been targeting a specific number, in this case 7.5. But maybe I should be "targeting" a range, in this case 5 at the lowest and 10 at the upper end?

Am I overthinking this? Should I just target 7.5 and make sure it doesn't sit a zero too long?

Thanks,

[Wasserpest]

For a high light tank (6W/gal??) you should target NO3 10 ppm, and see how quickly it drops below 5. Then you would be on average at 7.5... but test kits are not that precise anyway, unless you spend a chunk of cash.

If the kit is 100% correct and you find yourself dosing daily you could go higher in your levels, up to 15-20 ppm. But you need to be very sure about that, and even so, it might not be necessary. Observe your plants, and as long as they look green and healthy, and no algae appear, you should be alright with levels going lower than the "optimum" for short periods.

[scolley]

I should clarify on those lights... I've got a Current USA Orbit w/2 65w PCs. I only run one 65w dual daylight (6.7K plus 10K) most of the day. For the middle 4 hours though I turn on the other 65w Dual Actinic. I'm swapping that out for 6.7K this week. But either way, 8 out of 12 hours, it's only running 65 watts. So for a 20g tank, which seems to need a bit more light anyway, I don't really think it's a high light tank.

I go through 4-5 ppm nitrates daily, so "targeting" 7.5 with a range of 5 to 10 sounds like it makes a lot of sense. And it would work in my tank.

So obviously I do the same for phospates, just at 1/10th the amount? I'd like to say that I'd been targeting 7.5 on phosphates, but my kit is so hard to read, I find myself happy if it looks more than .5 and less than 1.0. Anything else is just too hard for my eyes to discern (not the best color vision).