Welcome to Reef2reef! It sounds like you're well on your way to a successful reef tank if you're willing to spend time learning!
I started out with a 5-stage RO/di system from
Bulk Reef Supply. I slowly upgraded it over the years, added the 150 GPH dual membrane kit, added additional canisters to make it a 7-stage, added a TDS meter, and added an Aquatic Life Smart Buddy booster pump. I will say in my eyes your water is the most important part of your reef. I continually upgraded because I wasn't satisfied with my water.
Now that I have experienced it all in stages, here are my suggestions for you.
1) Get a booster pump right away, I highly recommend the Smart Buddy, it automatically flushes, is contained in a nice looking and compact unit, and mine has been working flawlessly for 5 years.
2) As far as 5 stage vs 7 stage, 7 stage is clearly better but more so in terms of how often you change out resin. My 5 stage did a good job and would provide 0 TDS water no issues, but I would burn through a canister of Mixed bed resin in about 200 gallons of made RO/di water. Adding 2 more canisters allowed me to run Cation, Anion, and Mixed bed resins which led me to find out that I was burning through much more Cation than Anion. Now I can make closer to 1000 gallons of water before seeing 1 TDS register on my meter. I would recommend a 7 stage over a 5 stage but not above getting a booster pump if money is a factor. You can always upgrade down the road if you find yourself changing DI resin out frequently.
3) As I mentioned above, I was battling low output compared to how often I changed my filters, this lead me to adding a second membrane to turn my RO/di system from a 75 GPH into a 150 GPH system. Adding two membranes also cuts down on the amount of waste water created. I did notice a nice decrease in TDS coming out of the membranes which in turn also cut down on the amount of DI resin I go through. Its a good upgrade worth the money, but not needed at first.
4) Having a TDS meter is not an option anymore IMO. I thought it was when I first started but quickly realized that how am I supposed to know when to change my filters? Just get it, its super handy to have and takes the guess work out of it.
5) I added a float switch to my mixing barrel for about $15 and it was the best money spent. I once forgot I was making RO/DI water for 3 days... I didn't know until my utility company called me up saying I had a leak in my house.. Yup. True Story. Wife was not pleased, and my water bill was much higher than the $15 a float switch would have costed me. I ordered one that day and haven't had spilled water since. IMO, not optional. LOL
As far as mixing barrels go, I have two 34 gallon Brute trashcans with valves plumbed in to pull water out of each one but then a cheap pump to pull water from my RO/di bin and transfer it into my saltwater mixing bin. Once its full, I can close one valve and open another to turn the pump from a transfer pump into a mixing pump. Here is what I can say, its very nice to have, I would make some changes though. For my situation, 34 gallons just isn't enough but depending on your tank size, you may find different. Another issue is the pump size, I went with a 900 GPH pump, but I really should have gone 1500 GPH plus. It works, but slowly and sometimes I find myself having to manually stir up some salt that settles to the bottom. Lastly, I wish the bins were white. Judging by the 90/10 comment, you've been watching Ryan with Serious Reefs, you may have caught Ryan mention the white brute trash cans for mixing containers. White buckets and mixing bins are a nice thing to have to look for impurities but also any potential issues. I've done a water change a few times with new saltwater that was cloudy but didn't notice it in the mixing bin. I can also say I've mixed new water a few times only to find bits and chunks of buildup in my fresh saltwater. My gray brutes just hide too much for my taste.
To make this long post even longer, here are a few notes I can share related to RO/di systems.
Once silicates can get through your RO Membranes you'll often find Cyano start to pop up. I feel like this isn't something typically talked about when dealing with Cyano, but something I've experience and others have as well. Simply replacing your membrane and carrying out a few water changes has always done the trick for me without having to result to chemical solutions like Chemiclean.
If you pay attention to your tank, you can tell when your TDS raises from 0. Each tank is different, but ultimately shows signs. My tank in particular, I notice my goni's and a few particular patches of Zoas close up, and my meaty LPS like lobos and pectinia start to deflate and not look as fluffy. I will also notice patches of algea start to pop up. For me its usually a sign that I need to check my RO/di system and replace a few filters.
Finally, something to note, carbon blocks need to be changed out semi frequently. If you read the carbon block package, it's only good for 2,000 gallons of water with chloramines @ 1GPM or 3,500 gallons @ 0.5GPM. If your city water uses Chlorine instead, then it's good for 35,000 gallons @ 1GPM. But something that people confuse or overlook is the fact that this is total water. Many people forget that the carbon block is BEFORE the membrane which splits the incoming water into waste water and RO water. So that 2,000 gallons isn't 2,000 gallons of RO/di water, its 2,000 gallons of total water ran through the system. If you've got a 2:1 rejection ratio, that means you'll need to change the carbon block out every 666 gallons of RO/di water made. Again, that may actually depend on your flow rates and actual city water.
Hope this helps some, and again welcome to Reef2reef! Now I'm gonna go order some new filters for my RO/di system while I'm thinking about it!
