On city water, the choice between one tank and two is packaging and service design, not a personality preference. The Diamond puts 1.0 ft³ of 8% resin over 0.5 ft³ of carbon in a 10×54 tank on a single WS1 valve: one install, one bypass, one drain. Quote it when the home needs both softening and whole-home carbon in a tight mechanical room and the grain load fits a 30,000-grain class system. Quote two tanks, a Black Diamond carbon system ahead of a Diamond Soft softener, when the utility uses chloramine (catalytic carbon and more contact time), when the household's grain load or peak flow needs a larger softener bed (45K / 60K) or a larger carbon bed (1.5 / 2.0 ft³), or when you want carbon rebeds on a different schedule from resin. Start with the city's Consumer Confidence Report, then size.
This guide covers municipal water only. Nothing in it assumes a well.
How a one-tank carbon + softener is built
Layers, one valve, one regeneration path
The industry pattern is simple: carbon and softening resin stacked in one mineral tank, with one control valve running the service and regeneration program for the whole vessel. Softening still works by ion exchange on the resin bed; the carbon layer is the media class commonly used in the industry for disinfectant taste and odor on municipal water. The homeowner sees one tank, one brine tank and one valve to understand.
The Diamond, published specs
On The Diamond, the published stack is 1.0 ft³ of 8% crosslink resin over 0.5 ft³ of carbon inside a 10×54 jacketed tank over a gravel underbedding, with a 16×40 brine tank and a Clack WS1 five-button valve set up for downflow brining. Connection elbows are 3/4 in × 1 in PVC. In the field that means one bypass, one drain line with an air gap, one power drop, and one valve program to teach the homeowner. The exact carbon grade for chloramine cities belongs in the dealer documentation; confirm it in the portal before you quote a chloraminated supply as a one-tank job.
Where a one-tank combo wins
One tank wins on the jobs where the mechanical room is the constraint. A condo utility closet, a slab-home garage corner, or an HVAC closet that already holds the air handler often has room for a 10×54 and a brine tank, and not for a carbon vessel plus a softener vessel plus two drain stories. You set one WS1, one bypass, one drain with an air gap, and you hand the homeowner one valve to understand.
On a city-water quote where hardness and disinfectant taste or odor are both in play and the grain math fits a 30,000-grain class bed, The Diamond is the clean "good" or "better" line that keeps the install inside one visit. It is packaging and labor efficiency, not a claim that one tank outperforms two dedicated beds on every water. HVAC-led dealers will recognise the footprint argument from their own mechanical rooms.
Where two tanks win
Chloramine cities and catalytic carbon
If the CCR, or a two-pad chlorine strip at the tap, shows chloramine, the industry's usual answer is catalytic carbon with more contact time. That is why Aquonyx dealers reach for Black Diamond in the catalytic configuration, then a Diamond Soft softener downstream, rather than forcing every chloramine job into the combo. The media decision is covered in coconut vs. catalytic carbon.
Bigger homes and higher peak flow
If the grain-load math wants 45,000 or 60,000 grains, or peak simultaneous fixtures want more bed volume and lower pressure drop, quote the softener and the carbon as separate tanks and size each with its own tool: the softener sizing calculator for capacity, the home flow-rate (GPM) calculator and the carbon size guide for the carbon bed. Black Diamond is published in 1.0 / 1.5 / 2.0 ft³ on 10×44 / 10×54 / 13×54 tanks; Diamond Soft in 30K / 45K / 60K on the same tank sizes. Sizing whole-home carbon for municipal water covers contact time.
Separate carbon rebed schedules
Carbon and resin age on different schedules. Resin regenerates with brine; carbon is a consumable you eventually rebed. Separate tanks keep those service events independent, so a carbon change-out does not mean disturbing a healthy resin bed. Published rebed intervals are not on the product pages; take the interval from the dealer documentation before putting a number in the quote template.
Read the city's Consumer Confidence Report first
Before you pick one tank or two, read the utility's annual Consumer Confidence Report for that address. Pull three things: hardness (if it is in mg/L or ppm as CaCO₃, divide by 17.1 for grains per gallon), disinfectant type (free chlorine vs. chloramine; some reports only print a total chlorine residual, which means you call the utility or confirm at the tap), and any note that the utility switches seasonally.
Then confirm at the kitchen tap: hardness for the softener math, and a strip with both free and total chlorine pads if you need to verify chloramine. Free roughly equal to total usually means free chlorine; total up and free near zero usually means chloramine. That single fact decides coconut-shell vs. catalytic carbon on a two-tank quote, and it should make you pause before quoting any one-tank combo on a chloraminated supply until dealer documentation confirms the carbon layer. Use our guides to reading a CCR and chlorine vs. chloramine for dealers.
Size both ways: grain capacity and peak GPM
Softener side: people × 75 gallons × hardness in gpg gives the daily grain load; multiply by 7 for a weekly cycle and divide by 0.75 to select on usable capacity. Flow side: estimate peak GPM from the fixture count or a bucket test, then check each option against the dealer flow documentation. The city-water softener sizing guide walks the municipal version.
Worked example (labeled inputs, not a real job)
Example only. Inputs: 4 people, city water tested at 12 gpg, free chlorine on the CCR, peak fixture estimate 9 GPM, no iron on the tap test.
| Step | Calculation | Result |
|---|---|---|
| Daily water | 4 × 75 | 300 gal/day |
| Daily grain load | 300 × 12 | 3,600 grains |
| Weekly load (target about 1 regen/week) | 3,600 × 7 | 25,200 grains |
| Required rated capacity (÷ 0.75 usable) | 25,200 ÷ 0.75 | 33,600 grains |
| Published class at or above | Diamond Soft 45K | 45,000 grains |
Quote implication: this example's grain math already exceeds The Diamond's published 30,000-grain / 1.0 ft³ resin class, so the honest quote is two tanks: a Black Diamond coconut-carbon filter sized to the ~9 GPM peak via the GPM and carbon-size guides, plus a Diamond Soft 45K. Or tell the customer why a combo is the wrong fit. Run live numbers in the softener sizing calculator and the GPM calculator; confirm with a water test.
Install and WS1 service notes
Install point-of-entry after the meter and ahead of the water heater, with a bypass, a drain line with an air gap, and power for the WS1. On a one-tank combo you are programming one valve for the whole vessel; capacity and regeneration settings still come from the hardness test and household use, per Clack and Aquonyx dealer documentation. On two tanks, keep the municipal sequence: carbon ahead of the softener on city water so the disinfectant hits carbon first, as laid out in the municipal treatment sequence. For fault codes on any WS1, use the Clack WS1 error codes guide and resynchronise before you diagnose. Written Lifetime Limited Warranty terms provided to dealers.
How to present both options on the quote
Lead with the test numbers, then show both options side by side. Let the CCR and the grain/GPM math pick the winner, not the upsell habit. Leave price cells blank in the template; pull assigned wholesale and your installed price from the portal after approval.
| Option A, Good (one tank) | Option B, Better (two tanks) | |
|---|---|---|
| System | The Diamond: 1.0 ft³ 8% resin over 0.5 ft³ carbon, 10×54, WS1, 16×40 brine | Black Diamond (media per CCR) + Diamond Soft (capacity per sizing) |
| Footprint | One mineral tank + brine | Two mineral tanks + softener brine |
| Fits when | City water; hardness + taste/odor; grain load inside the 30K class; tight space | Chloramine; higher grain load (45K/60K); higher peak GPM; separate carbon service |
| Install | One valve, one drain, one bypass | Two valves (as shipped), carbon ahead of softener |
| Service | Single WS1; carbon and resin in one vessel | Carbon rebed and softener service on separate clocks |
| Your price | Dealer portal | Dealer portal |
| What a new dealer needs | One tank (The Diamond) | Two tanks (Black Diamond + Diamond Soft) | Edge |
|---|---|---|---|
| Mineral tanks | One 10×54 jacketed tank. | A carbon tank (10×44 / 10×54 / 13×54 by volume) plus a softener tank (by capacity). | Depends |
| Media (published) | 1.0 ft³ 8% resin over 0.5 ft³ carbon. | Carbon 1.0 / 1.5 / 2.0 ft³, coconut-shell or catalytic; softener 1.0 / 1.5 / 2.0 ft³ resin (30K / 45K / 60K). | Depends |
| Valves | One WS1 five-button downflow brining valve. | A WS1 on each system, as shipped (metered on the carbon, downflow brining on the softener). | One tank |
| Brine | 16×40. | Softener brine 16×40, or 18×40 on the 60K; none on the carbon. | Depends |
| Connections | 3/4 in × 1 in PVC elbows. | Same pattern on each system, per the product pages. | Depends |
| Best fit on city water | Tight space; hardness plus free-chlorine taste/odor; a 30K-class load. | Chloramine; larger grain load or peak flow; separate service clocks. | Depends |
| Primary trade-off | One footprint and one service point. | More footprint; independent media life and sizing. | Depends |
Specs are the published figures on each product page. Flow ratings and rebed intervals come from dealer documentation.
Dealer FAQs
Carry both options as an Aquonyx dealer
Aquonyx manufactures The Diamond, Black Diamond and Diamond Soft in the United States for independent dealers. There is no application or franchise fee; approved dealers start with a one-pallet opening order and assigned wholesale pricing in the portal, with product and installation training during onboarding. Apply to become a dealer, see the whole-home filtration systems and wholesale water softeners, or call (888) 295-3339.
This guide covers municipal (city) water. Equipment is described by type and published specification only; the model's dealer documentation states what each system is designed to do.
About Aquonyx. Aquonyx builds city-water treatment systems for independent dealers. You buy from the maker. Articles are written and reviewed by the Aquonyx Technical Team; see how we source and check them.