On Sunday I did my usual 50% water change (10 gallons) and add 10 gallons of DI water from my LFS, then proceeded to dose my EI fertilizers. I treated the water with Prime before adding. I heard I had to mineralize the water before adding? Can someone explain this?

I asked the LFS and they said I have to do this with RO water, not DI?

Distilled and Reverse Osmosis water are "filtered" into basically pure H2O it is just done by different methods. One a fine membrane, the other vaporizing water into steam and collecting it later minus other minerals and contaminates. IDK why they would say that one requires mineralization over the other. Seems like they just made that up. However, if you're going with 100% RO or DI water you will need to add minerals back into the water. Ex. a GH booster. Or just mx 50% tap 50% distilled or RO water. Thats what I do and many others. Are you using 100% that water and for what purpose?

Well right now, its 50/50, since I only did 1 water change and I just started this on Sunday. From here on out Ill be using DI water, so eventually the tank will be all DI. I bought a tub of GH Booster from GLA and it arrived yesterday and I will be dosing that upon my water change, for the rated amount (1/4 teaspoon) OR dose the GH Booster when I dose my Macros (Sun, Tues, Thurs @ 1/32)

I am doing an experiment. Ever since moving to my apt, Ive had BBA. Ive done everything ever written on BBA to try an eradicate it on any forum I found. Bought new lights, raised lights, less light, more ferts, less ferts, more CO2, more flow, Excel, H2O2, and one thing I didnt change was my water. Thats the whole reason behind my 'experiment' so see if it goes away or stop showing up on my plants.

I believe he means De-Ionized or softened water, in which the GH hardened ions are exchanged for sodium KH ions in a special filter.

Since sodium really has no use as a plant nutrient it's not so good, you would be better off thinning your normally hard municipal tap water with RO water. The Calcium and Magnesium carbonates and GH ions will be used by the plants and the overall pH and KH will be a bit lower.

So instead of doing my 10 gallons of DI.. You're saying do 5 gallons of DI and 5 gallons of my tap? I was under the assumption that RO water was suited better for saltwater tanks

Depends on what kind of KH/GH balance you want to achieve, 25% tap to 75% RO would also work. Have you tried testing your tap water yourself to get a baseline? RO water is what's almost overwhelmingly used in planted freshwater tanks in areas with hard water out of the tap. The extreme alkaline pH of DI water would seem cause a lot of problems with Ammonia/Ammonium ratios and the uptake of certain chealated micro nutrients. Also IIRC, sodium ions throw their own effects on nutrient availability, possibly causing element deficiencies.

Years back in the early years of high tech planted tanks, Sodium Bicarb was considered OK for boosting KH in really soft waters, but we've progressed a bit since then.

That could make sense.. I do have a GH & KH test kit. Back when I tested maybe a month ago, my kH was 3 and my GH was 18, tank water, not the actual faucet I get my water from (Just using API kit) I havent tested since then since 1) I dont understand that relationship. 2) Plants are growing & fish are very active, so I put that on the back burner.

Where I live, I have the enviable, ( and highly debatable ..) advantage of having darn near rain water coming out of our taps, although there's a bunch of silicates and tannins. Our water out of the tap is pH 6.3 right now, with about 2 GH and nearly unreadable KH ( tested with API DH/KH test kit.) I have to nearly fully mineralize my water to make it a happier, plant growth conducive environment.

Not sure what the accepted GH/KH optimum balance for most successful planted tanks is, somewhere like a KH of 2~3 and and GH of 4~6...?

I would take having to thin my water with RO over what I have to do right now.

CO2 injection always helps, which because CO2 dissolves to become Carbonic acid, which helps with keeping your tank's pH at a somewhat stable, slightly acid baseline that is always a first good step because of the availability of Ammonium vs. Ammonia at this pH.

Plants will use either form, but they really like Ammonium, it involves less energy to use than Nitrates, also availability of Fe ( ionic iron..) at the hair root level occurs more easily when your water is in the 7.1 to 6.7 pH range. Having the gravel bedded with a good load of beneficial micro critters helps with this uptake of nutrients.

It's a bit of a balancing act, but not a difficult one to maintain once the tank comes 'online'.

These are kind of a basic guidelines for where you want your water chemistry to be to allow the tank to run with nice plant growth, there are other things that come into play, but for basics, *please don't use DI water* it'll throw your pH into wacked out swings and cause nutrient deficiencies.

Wow.. thats a great explanation. I know my LFS has RO water, so I will switch over to that eventaully and slowly. Since I have the GH Booster, I assume I wouldnt need to use any other product like Seachem Equlibrium?

I would consider your tap water to be near perfect for a mineralized base except that it could use a bit more Magnesium and Potassium.

Mg is easy, Epsom salts at the pharmacy or variety/foodstore I get mine at Safeway.

Beer homebrew shops sell Potassium Sulfate as do Hydroponic stores, or order from GLA or Amazon. Good to get food grade if you can find it.

Was looking into RO myself, RO Buddie 3 stage. Wanted 4 stage with the DI. Reason is that it supposedly can get rid of the Chloramine in my tap water.

So if DI is not good for planted tanks then my other option is dual carbon filters. Otherwise, I could get a big trash can fill with tap and wait out the Chloramine. From my reading that could take a month.

Just wanted to run that info by you cause all my reading gives a lot of sometimes conflicting info. So DI is out. Maybe the carbon filter in RO Buddie will help, dunno.