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Until now, I have been using a R/O filter given to me by a friend for my L046 zebra tank water. I would add Replenish, by SeaChem, to replace the minerals removed by the RO filter. I've bought a RO/DI filter and was wondering if Replenish is good enough for the addition of a DI filter? I've never dealt with DI water and wanted to make sure it is safe for fresh water fish with just the addition of Replenish.

Also, is there a more economical mineral additive out there? Thanks for your suggestions.

I've had good luck with SeaChem RO/DI mineral supplements to be fine products but most of the time I use a blend of RO/DI with however much tap water it takes to reach the target readings you seek,
The latter is cheaper and easier.

I also just mix in tap to get the readings I need. It is pretty easy to make a chart to track pH, GH and other values for 10%, 20%, 30% tap water to RO/DI water. Keep in mind that your tap may fluctuate over the year depending on its source. My county water source is the Potomac so values drop slightly after heavy rains.
-Shane

I noticed that you live in Minnesota. If you have well water and you have liquid iron like mine, mixing with tap water may not be a good idea. Pseudacanthicus, for example, do not do well with the iron. Obviously you will need to use more Replenish.

If you do not need to make a lot of water liquid products are the way to go. I need a lot of water daily so I have been using RO Right powder for years. One needs to shop around to find the best price. I tried the liquids for a month but the cost! There have been a lot of comments about their product and what is in it over the years but hey my Pseudas like it along with Discus!

Jim

If you have plants in your tank Seachem's Equilibrium would be a better option than Replenish. To raise your KH though you'd need something like the Akaline buffer (with possible addition of the acid buffer) if you notice your pH is raised. I used these options for a couple years since our tap water is not reliable and it kept the water parameters very stable. There is also the other line the 'carbonate'for KH and 'mineralize' for GH from AquaVitro, these are both liquid so if you automate your water production they're easier to incorporate with a dosing pump than the powdered ones.

I would argue that RO water is perfectly safe for softwater plecos without additives, providing you change the water regularly to avoid excessive build-up of acids. See this post for some more details. Adding a little permanent calciferous material to the tank is another option instead of expensive additives. I think @Jools uses oyster shells?

I also don't think a DI is necessary. Maybe for the reef aquarium, but not for plecos.