Hi I'm an idiot, but I can grow successfully in DWC so here are a few thoughts and suggestions I'd like to make that might help beginners out. I'm not going to bother going over how to make a DWC system, there are already some fine threads about that topic. I'm just going to touch on some concepts and day to day issues that as a DWC grower you will have. I might add more later and if you have any questions it's best just to pm me.
I'm assuming for my convenience that you are using GH nutes and the Lucas formula (search it) but the same principals apply to what ever nutrients you are using.
Transplanting
So you’ve started your seed in a rock wool cube or starter plug and the roots have started to break out the bottom. At this point some people will transplant them right into their garden, only problem is that the roots are not long enough to reach the water. I like to have my roots long enough to reach the bottom of my net pots to ensure that they aren’t going to be starving for water.
In soil they start in small pots and transplant up in size. I do the same thing by taking a Dixie Cup and cutting holes in the bottom and filling it with hydroton (small size) and putting the seedling in there for about a week.
You can then place the Cup so that it is half submerged in a bowl of water. Change the water regularly and within a few days the roots should be long enough to transplant to your DWC system.
Proper Water Level
After you transplant your seedling into your DWC bucket or tub you want to keep the water level a few millimeters above the bottom of your net pots. An easy way to make sure is to put an empty net pot in first and add the water through the pot till its just filling in the bottom. Even though hydroton does have capillary action if you keep the water below this point your new seedling or clone might not get enough water and die.
Your roots will grow down into the nutrient solution. Let the water level drop naturally over the next week or so till you have about a 3~4 inch air gap between the bottom of the net pot and the top of the water. The roots above the water will turn into air roots and the ones in the water will remain water roots [after talking with another grower there is doubt that the roots above the water are actually air-roots, just seems to be a common term that many people use, the terminology is probably incorrect but the method is sound]. This will help act as a barrier to protect the plants from disease. Many growers experience pythium even if their water temps are in check because stale water within the net pots is warmer and it’s a perfect breeding ground for it. Once you have this air gap you will want to keep the water level constant for the remainder of your grow by adding water back daily.
In this pic you can see that my nutrient solution is just above the bottom of the pots. This clone has been in there for about 3 days and the roots are already coming out. Over the next week I'll let the nutrient level drop and create the air gap.
After a few weeks the roots will look like this and the water level will drop creating the air-gap. I've marked the water line with a permanent marker and will keep the level here for the remainder of the grow.
pH
People really stress too much over Ph. They allow themselves to become further stressed by people telling them their levels are too low or too high. The reality is that marijuana is happy at a wide range of ph. Anywhere between 5.0 and 7.0, it even tells you this on the back of your GH nutes bottle. These nutes have a buffer in them; which will drop most tap water (assuming you tap is not hard water and comes out of the faucet around 7.0) to about 6.0. What this means is that you will most likely never need ph up/down or a Ph meter to test your water. Of course you have to make sure that your tap water is acceptable to use in the first place. You can buy a paper test kit for a few bucks, that’s right, a few bucks. If your tap water doesn’t taste hard and it’s near 7.0 pH out of the tap you are golden. You should test it when the seasons change or every few months because many places use different sources for their taps at different times of the year and it might change a little.
Rez management
When we talk about rez management we are talking about when to add water to your rez, when to add more nutrients and when to dump it all out and start over again. Every day your water level will drop due to evaporation and the plants drinking it up. Everyday you should add the same amount of water, which has dropped so that you keep it at a constant volume. You should take notes on how much you add back every day. If your using a 50-liter rez and every day it drops 5 liters, then you must add 5 liters back. After 10 days you will reach 100% addback, meaning that you will have added the same amount of water, which you started with. Here are 3 strategies that you can use to manage your rez
- 1. Add plain water + dump at 100% addback; this is the easiest method and is a good place to start for beginners. You add back plain tap water and once you reach the amount you started with you drain your rez completely and mix a new fresh rez and start again. You repeat this till the end of your grow. The plus side is you don’t need to measure your ppms with a pen and it’s easy to remember. The downside is that your plants are not getting a full meal most of the time.
2. 33% nutes + 100% addback: This method you are going to be replacing the food as well as the water with your daily toppings. Some smart people figured out long ago that the amount of food that the plants eat everyday usually equals 33% of the amount needed for the volume of water which is missing. So if you are adding back 1 gallon of water, instead of mixing Lucas formula at full strength for that one gallon, you only add 33% for that one gallon you add 2.64ml of micro (8ml * .33 = 2.64ml) and 5.28ml of bloom into the gallon of water and add it to your rez. Everyday you do the math for the amount you add back and once you reach 100% addback you drain the rez and start from scratch again.
3. PPM readings + 100% addback: Very similar as above, but instead of trusting that your plants have eaten 33% of the nutrients of the dropped water volume you use your ppm pen and find out how much they have actually eaten. It’s best to top of your rez first and let it sit for a while to get an accurate reading. Lucas formula is 953ppms 0.5 so if your reading is 800 ppm than you should be adding back 16% (800/953=0.84 or 16% less than 100%) of the total volume amount. So if you have a 20 gallon rez that would work out to 20*8ml*.16=52.8ml of micro and twice that for bloom. If this confuses you stick with the first options. Once again you drain your rez at the 100% addback point and start fresh.
A lot of growers don’t bother changing their rez during a grow. My advice is that a fresh rez is always better than one that’s been used and added back to over months, so I’d stick to dumping at the 100% addback.
Heat / Water temp
Heat is a major concern with all growers in hydro but is of particular concern for DWC growers because unlike Ebb&flow/NFT/Aero there are no dry periods and it’s very easy for pythium to take hold. Water warms up and cools down slower than air but will eventual match the air-temp of the garden. The problem is that you want your daytime air temp in your garden to be around 70-80 degrees and 10 degrees lower for night temps. Pyhtium really becomes a problem above 72 degree but for safety you want to keep your water temps below 69. There are 3 ways you can deal with this problem
- 1. Frozen water bottles: You can freeze water in empty coke bottles and put it in your reservoir to temporally lower the temperature. The plus side is it’s cheap and effective, doesn’t use electricity, and is quite. The down side is that you will have to keep an eye on the temps and will probably need to do it a few times a day.
2. Fan in the reservoir: By blowing air across the water evaporation takes place and the water’s heat is the energy that is used to change the state of the water. You can lower the water’s temp by up to 6~8 degrees with an aquarium fan they sell at any pet store. The plus side is the fans are cheap, you probably already have on you can use and it doesn’t cost much to buy one. The down side is that the amount you can drop the temp is limited and it also increases the humidity in the garden, which can be unwanted in some situations.
3. Aquarium Chiller: Chillers have coiling coils in them which water is pumped through and cooled. They come in different sizes and range from 50 liters to hundreds of liters in cooling capacity. The plus side is that they give you accurate control of the temperature and freedom since you don’t have to constantly check the temp like you would with frozen water bottles. The down side is that they are expensive and use as much electricity as a small HPS light. You’ll also have to buy a water pump to put in the reservoir, which again is added cost and electricity.
The rewards for keeping your water temperature in range is a greater yield and elimination of the #1 reason for failure for DWC growers; Pythium.
