FF Sledgehammer usage

I’ve been loosely following the FoxFarms dirty dozen feeding schedule now for a while.It mentions using Sledgehammer to flush between weeks 4-5, but I’m conflicted on what they mean by flushing… Instructions say to use 2 teaspoons per gallon, but on the other hand the definition of flushing I read of in the forum says to use roughly 3 times the amount of water vs soil to flush. The more I read on Sledgehammer, the more it sounds like a typical watering instead of a true flush. My plants seem to be doing ok for the most part. One looks slightly nute burnt, but is still shoving out nice fresh growth. I’m about at the stage for this Sledgehammer flush, but I don’t want to goof it up. Just mix a gallon, ph it and water as usual or will I be flushing my 7 gallon pot with 21 gallons of water making sure ph and sledgehammer are in each flush? And… When setting PH… I’m assuming it should be at 6.5 for my soil grow after the sledgehammer has been mixed in, correct?

I know for flushing my FFOF it’s been said for a 5 gallon bucket to flush 15 gallons of tap water. I only started doing that on my Blue Dream I already harvested. As our tap water is heavy with chlorine, I will let the buckets rest a couple of days after flushing. Then it’s game on with the flushed soil.

For the record I don’t do pH nor use anything added to flush…just plain tap water.

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Sledgehammer is a rinsing agent that grabs on to the nutrient/salts so it takes a lot less water to perform a flush. I slowly pour in the water with sledgehammer and let it sit 30min to an hour. Then follow up with plain ph’d water (usually 2 gallons) until my ppm’s are close to the water Ppm’s that’s being put into the soil. Once the Ppm’s are right, go back with a gallon of your nutrient solution


Awesome info. Thanks you both for that! I’m on a well, so no worries for the chlorine, but my water ph’s out at around 8.4 - 9.0 right out of the tap, so I think there’s a lot of something in it. I think I’ll mix a gallon of the sledgehammer up and PH into the safe range at least before using. I think I’ll forego the super flush for the time being and just do the gallon of sledgehammer, then plain PH water after. Similar to @BobbyDigital
I really appreciate the replies.

Sorry for asking but… where do you live that you ph is that high?

If the solids are low enough, almost anything can drive the PH up or down. But it wouldn’t require much to bring it back down. For example: try reading distilled water. It will be all over the place as there are no solids to read.

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I’m around southern Virginia, North Carolina-ish. Yeah… I was not ready the first time I ran a PH on my water. This was a brand new meter that was calibrated just before the test too. I figured well water would have some minerals and other stuff in it, but that’s a pretty high number. Am I correct in assumiing there’s a lot of solids in there?
@Myfriendis410 … I do want to get some distilled water so I can test the soil runoff and just get an idea where my nutes should be. Funny… when I add nutes and test PH, it’s usually just about right on the number around 6.5, but I am seeing what looks to me to be some mild nitrogen burn. slightly clawed leaves. It’s making me think I should monitor TDS which is something I haven’t yet done.
I just flushed with a gallon of Sledgehammer that was PH’d down to 6.3. I think I’ll hold off on any further flushing until I have a look tomorrow.

You’ll want to flush out that sledgehammer. Or it will absorb all the nutes you put back into it.

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Ahhh… OK. I will do that first thing tomorrow. Tent’s about to go to bed for the night. Thank you!

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Better to do it now, sorry. You don’t want the roots soaking in media any longer than you have to.

TDS is incredibly important and something that you should be monitoring closely. The fact your nutes PH into range tells me the water is likely under 200 ppm (nice clean water). Mine from the city supply is 550!

I bought the R/O Buddie and make my own water to eliminate that as a variable. Unfortunately you do have to account for the solids latent in the water.

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I didn’t mention I am doing a soil grow, so the roots will most likely be wet no matter what. I did make it out and got in a quick flush before the lights went out though. I will get it again in the morning to finish up. I’m also using those air pots so hopefully, it should aid in drying out more quickly. The plant seems to be holding it’s own at the moment. Slight claw, but no burnt or dying leaves. A little droopy though. I have two white widow autos in with it that are doing really nice. No issues.
For some reason, I was under the impression my water might have high mineral content or more solids because of that high PH. You say it’s probably clean? I’m relieved to hear that. Just moved here from the city. Dunno a lot about well water. Guess I’ll run some and do a tds on just plain and have a look. This is not my first indoor grow, but I am new to some things, like tds. I can also see how it can be important. I appreciate your input!

Hell of a bush! She looks overwatered. She drying out completely before watering?


Over watered and some N toxicity. I would avoid any supplements containing nitrogen for now. You do have to let the soil dry out between waterings. This will avoid issues.

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I was afraid I was over watering. Been going off how heavy the pot feels. for whatever reason, this plant’s pot always seems to feel lighter compared to the two white widow auto’s I’m also growing. They’re smaller plants and doing very well, but their pots always feel heavy compared to this one. I’ve been giving very light watering to them and heavier to this big plant thinking it’s bigger and going through the water more quickly. Also read these air pots tend to dry out more quickly. Looks like I’m over-reacting. I haven’t watered since flushing two nights ago. It’s looking better, but still some leaf curl. It’s also been about a week since any nutes. I did recognize they could be a problem. I’m going to really allow them all to dry out more before watering. Maybe skip again and see what tomorrow brings. No nutes at all. Just ph’d water for a bit. @Myfriendis410 & @Bobbydigital… Thanks very much.

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I’m only going by the fact the nutrients PH to the correct range in GH: if it was high in solids (TDS) I would expect the PH to be off. But you really need to test and monitor all of your water.

I would expect that plant in that sized pot to go four or five days between watering. You can run her out until she’s just starting to wilt before watering again. You want to give the plant a complete wet to dry cycle at every watering.

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Ok… Today is third day without water and the plants, all three are looking good. Learning my lesson on the watering. Thought I was doing alright up until this, but seeing now, I was goofing up.
I think you’re right on the water quality also. I tested a sample from the faucet and ppm was swinging around. Anywhere from 81 to 300 ppm. Closer to the 81 than the 300. Was mostly in the 81-110 range. I figured there was a high solids content mainly from changing the filter once a month. It’s always covered in some nasty smunge and water pressure drops off pretty quick when it’s time for the new filter. I guess it’s doing it’s job.

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Just for instance: my water is 550 ppm

@Myfriendis410, @MattyBear I have 5 plants with runoff pH @ 6 . However, my ppm is 1700 for 2 plants and 3@ 2300-3500. Used to be 6000ish. I red that 1700 is OK. They are growing healthy I think.

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As long as they are healthy, that’s the most important thing. FFOF is a hot soil and has a lot of stores nutrients. Some plants can handle it and some will burn.