Pool Math Question/clarification

[LakeLizard]

Per my signature, I have an H2X SwimSpa so I understand this is though of as a large hot tub/spa?

The question/clarification I have is when setting up pool math; do I use "traditional spa" or troublefreepool.com" goals?

I am currently using 8.25% bleach as my sanitizer.

The other question I have is; according to pool math plugging in my actual readings, the CSI states the spa water "balanced" 0.05.

Here are my current readings;

FC-4.5

PH-7.5

TA-80

CH-400

CYA-50

Borate-50

Temp-89 deg

Using goals for trouble free pool.com

Should I be concerned about the CH being at 400 even though CSI says "balanced"

Just looking for validation, if you will.

Thank you,

LakeLizard

[chem geek]

For a spa you don't have FC goals the way one does for a pool so the setting doesn't matter since you won't be looking at those goals. Instead you will add whatever amount of oxidizer or chlorine after your soak that you need so that you still measure a residual FC 24 hours later. If you aren't soaking every day, then you can target a roughly 2-4 ppm FC with 30-40 ppm CYA and then shoot for ending up with around 1-2 ppm FC just before your soak. Spas typically don't get algae because they are covered tight with no light and also high temperature.

The CSI won't be balanced when the temperature gets higher as you'll see when you input 104ºF instead. The CH of 400 ppm is high so you'll need to get your TA lower to around 50 ppm which will help. Is your CH high because of your fill water? If so, you could consider using a pre-filter when you fill the spa next time though keeping the TA lower should help. The main risk is if the pH were to rise -- if you kept your current TA and had the temperature higher and the pH got to 7.8 or higher, you could get calcium carbonate scale, especially in your gas heater.

[LakeLizard]

Thanks chem geek.

I've made some adjustments and would like confirmation if you (or anyone) please;

Spa Side - 225 gallons at 102 degrees

FC-4

PH-7.5

TA-50

CH-350

CYA-50

Borate-50

Swim Side - 2045 gallons at 89 degrees

FC-4

PH-7.4

TA-50

CH-400

CYA-50

Borate-50

Hopefully I've finally hit the "sweet spot"?

Thanks again for all the great advice and explanations.

LakeLizard

[chem geek]

Yes tat looks reasonable. If you had separate bodies of water that didn't mix, you'd want your CH lower in the smaller hotter spa than in the swim spa that was cooler. Calcium carbonate saturates more and has more risk of scaling at higher temperature. If you keep your TA low as you have and watch the pH you should be OK. Does either the swim spa swim side or spa side have any plaster or grout exposed to water? If not, then there's no need for CH to be higher than about 150 ppm where that amount helps to prevent foaming.

[LakeLizard]

@chem geek

Unfortunately due to what I assume were inaccurate CH readings from my previous Lamotte test kit, I had increased the CH levels in both chambers. My next water change in a few weeks, I will likely end up with much lower CH levels.

There is very minimal water exchange between the two chambers, maybe up to ½ gallon either way due to vigorous swim or when two or more soak in the spa side (spill over).

The swimspa is fiberglass (I assume) so there is no plaster or grout to be of concern.

As mentioned, when I change the water in a few weeks, my readings will be more in line.

Water balance can be very challenging when relying on an electronic tester you assume to be accurate. Now that I have a Taylor T-100 kit, I look forward to more favorable results..

Thanks again for your wisdom.

LakeLizard

[chem geek]

I think you mean the TFTestkits TF-100 that is based on the Taylor K-2006 and uses the same reagents (except for pH it uses the Taylor K-1000 equivalent).

[LakeLizard]

@chem geek,

Given my readings from above, am using bleach as my sanitizer maintaining 3-4 FC and <.5 CC. Usually swim for 15 -20 min on the 2045 gallon side on average 3X per week, then soak for bout 15 min in the 225 gallon side fight afterwards. Am I understanding that I should be using oxidizer in addition to bleach? If so, what's your recommendation for frequency of oxidizer given the parameters mentioned herein? Not seeing a formula in pool math to help with amounts and results.

Super happy with the crystal clear water and the feel so don't want to knock anything out of balance with excessive oxidizer.

Thanks again for your patience and explanations.

LakeLizard

[chem geek]

No, the bleach is your oxidizer to handle your bather waste. Basically you just want to add whatever amount of chlorine is needed to maintain a residual. The difference between residential pools and spas is that pools generally have a big enough water volume that the bather load is negligible and most chlorine loss is from sunlight. So the amount of chlorine to add is pretty consistent each day unless you have cloudy days. For a spa that is much smaller in volume, the bather load is typically much higher and the amount of chlorine that needs to be added is proportional to the bather load except for the days in between soaks in which case the chlorine loss is at a fixed proportional rate.

Your swim side is sort of in between. It is affected by bather load, but not too much. So just add enough chlorine to maintain a decent chlorine level. If the swim spa is uncovered then PoolMath does tell you the FC needed for a given CYA level to prevent algae growth (be sure and set the "troublefreepool.com" setting in the lower section). That is, you can treat your swim side like a small pool.

As for your spa, people usually prefer soaking in less chlorine so you can target adding enough chlorine after a soak so that you have 1-2 ppm FC for the start of your next soak, though it's up to you if you want to go higher.