I also measured mine (Blue DE scoop from Leslie's Pool Supply) at 11 oz/scoop (that is, 0.69 lbs/scoop). At first I was using a number of 0.6 lbs/scoop and that threw me off by a surprisingly whole lot. I was adding 10 scoops thinking I was adding 6 lbs, but 10 scoops at 0.69 lbs/scoop is 6.9 pounds. Instead I should have been adding 8.7 scoops, meaning I was overcharging by over an entire scoop. When recharging after backwash I should have been adding 4.8 lbs, which would be 7 scoops but instead I was adding 8 scoops, again overcharging by a whole scoop…. [W]hen I broke down my filter after only a short time of use it was clogged with DE bridges, the lesson learned being that I should be more precise in my measurements and I don't want to overcharge it.
I don’t think an extra pound here and there spells disaster — in your instance, that’s about 15%. That said, there’s possibly a cumulative effect over time, which may be what occurred in your case. In general, it’s better to err on the side of undercoating, as overcoating tends to decrease filter efficiency substantially with not much of an increase in filtration efficacy, whereas with undercoating, harm to the grids/fingers/filaments doesn’t really occur until you reach near zero filtration media.
>TishTash Jul 16, 2020
>My Hayward EC65A filter officially specifies 6 lbs of DE for its 27 sq ft of filtration area.
Are you sure about that? That sounds like a whole lot of DE. My Hayward DE4820 DE filter says only 6 lbs for its (twice yours) 48 sq ft area.
This is why the “one-lb-for-every-10 (or 7 or 6.25463)-sq ft” rule is silly: This one happens to be “1 lb for every 4.5 sq ft”! Just follow manufacturer’s instructions and all will be well:
DE filter instructions warn users not to run the filter for an extended time if it's not charged with DE. They say only two or three minutes. They don't say why not and I've always wondered why not. My theory is that running dirty pool water through uncoated grids causes dirt to stick in the grids, resulting in a problem. But I don't see that as "perrmanent." Worst case is that your grids perform poorly until the next time you break the filter open and soak the grids in TSP and brush them down during their yearly deep cleaning.
I’m no expert, but aside from subpar filtering, sufficient dirt and oils adhering directly onto grids/filaments/fingers probably renders DE coating less than optimally, and will also degrade them over time.
That said, I hardly soak the filaments of my EC65A, much less annually, since they’ve been filtering fine and going back to the same pressure after a decent backwash — which I beg to differ isn’t such a difficult thing, especially since I backwash once after a SLAM, and then not again until I winterize 5 months later. But YMMV.
>Diatomaceous Earth has a density of 20 lbs/ft3 (unpacked). That translates to 1 lb of DE = 48 oz, which is 3 fluid pints (16oz/pint) or 6 fluid cups (8oz/pint)
Taking TishTash's word for it that the rest of it is correct, the last part of the above is wrong. Instead of "6 fluid cups (8oz/pint)" that should say "6 cups (2 cups/pint)."
My bad; I meant to write “8 oz/*cup* … but I prefer your parenthetical edit.
>Remark37, May 21, 2021
> If I go by the weight with a scale, 11.2 oz of de/scoop
^^^THIS!^^^ Use a scale to determine how much DE your scoop holds.
This is ultimately true, but knowing 1 dry lb of DE (by weight) = 48 fluid oz (by volume) renders obsolete all those magical scoops promising they measure exactly 1 dry lb of DE — which both of you have shown is demonstrably false: Last time I checked, 12 dry oz does not equal a dry lb (16 oz).
>TishTash Jul 24, 2024
His point #3 recommends just using a measuring cup with a number of 3 cups/lb of DE. ASsuming his numbers are good, his method may be ok if you use a 4 cup measuring cup, which is an unusual item. But I don't like his suggestion to use 18 cups of 14 cups. That's because I think backwashing and charging the filter is a time consuming chore that needs to be made as easy as possible, and I have found that if a job can be simplified even a tiny little bit, it makes a big difference. Scooping 9 or 7 scoops is easier than scooping 18 or 14 tiny scoops, and I'm sorry but I do not like scooping DE. The lesson learned there is that the bigger scoop is less work and that's a win.
It’s worse than that: It’s 3 fluid *pints* per dry lb of DE (or *6* fluid cups per dry lb). I certainly wouldn’t use an 8 fluid oz cup and count to 28 or 36, and I have to agree 14 to 18 of a fluid pint-sized scoop is still unwieldy. Dammit, I *should* look for a 48 fluid oz scoop and have to dump only 5–6 of them. If you think that’s silly, I’d say what’s sillier is trying to base one’s calculations on a scoop that measures 12 dry oz of DE, when it’s far more elegant to start with 16 dry oz of DE — which is magically … a dry pound! (vs 3/4 of a dry pound which is what that magical scoop really is).
And finally, all those people above that are trying to calculate the weight by starting with the density of DE or how much per cubic foot, etc. Bleah. In my book weighing it with a food scale and knowing how much DE your scoop uses, to the tenth of a pound, is the best way.
As one of “those people,” all I have to say is, “You can lead a sore to pool water, but you can’t make him think.”
