Domakihub How to Lower Pool TDS and Restore Crystal-Clear Water
High TDS makes pool water dull and corrosive even when your pH and chlorine look perfect.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
Total Dissolved Solids accumulate in pool water over time from sunscreen, body oils, minerals in fill water, and chemical treatments — and no amount of shocking or pH balancing will remove them. The video above walks through exactly why TDS becomes a problem and what your only real options are. This guide gives you the step-by-step process for homes, holiday rentals, and hotels across Greece, where hard tap water and heavy summer use push TDS up fast.
What TDS Actually Is and Why It Matters
TDS stands for Total Dissolved Solids — the combined weight of everything dissolved in your pool water that is not H2O itself. This includes calcium, magnesium, sodium, chloride, cyanuric acid, bather waste, and every chemical you have ever added. A healthy pool typically sits below 1,500 ppm; once you exceed 2,000 ppm (or 1,500 ppm above your fill-water baseline), water quality deteriorates.
High TDS does not always look alarming on a basic test strip. Your pH might read 7.4 and your chlorine might look fine, yet the water appears flat, slightly green or brownish, and refuses to clear up no matter what you add. That is the hallmark of a TDS problem: the chemistry looks acceptable on paper while the water performs poorly in practice.
Why You Cannot Simply Add a Chemical to Fix It
This is the point most pool owners miss. Every chemical you add to correct another problem — acid to lower pH, algaecide after a bloom, extra stabiliser — contributes more dissolved material. You can never chemically treat your way out of high TDS; you can only dilute or replace the water. In Greece, where municipal fill water is already moderately hard and evaporation is intense through summer, TDS climbs faster than in cooler climates.
Some service technicians sell flocculants or clarifiers as a TDS solution. These products can temporarily improve water clarity by clumping particles together for filtration, but they do nothing to reduce the actual dissolved-solids count. Knowing this saves you money and frustration.
How to Lower Pool TDS: Your Step-by-Step Plan
- 1
Test Your TDS Before Doing Anything Else
Use a digital TDS meter — not a test strip — to get an accurate reading of both your pool water and your tap fill water. Record both numbers. The relevant figure is how far your pool exceeds your fill-water baseline, not just the raw pool reading. If your fill water itself reads 600 ppm and your pool reads 2,300 ppm, you have 1,700 ppm of accumulated solids to address. This baseline comparison tells you whether a partial drain will be sufficient or whether you need multiple cycles.
- 2
Calculate How Much Water to Drain
There is no chemical shortcut here: dilution is the only mechanism. To halve your excess TDS, you need to drain and refill roughly half the pool volume. For a 50 cubic metre pool that means removing around 25,000 litres. In practice, most pools benefit from a 30–50 percent partial drain, which brings TDS back into a manageable range without fully emptying the vessel. Use an online pool-volume calculator if you are unsure of your pool's exact capacity.
- 3
Drain Partially and Refill with Fresh Water
Turn off your pump and use a submersible pump or your pool's waste port to remove the calculated volume. Drain slowly to avoid destabilising the pool shell, especially for fibreglass or vinyl-lined pools on clay-heavy Greek soils. Once drained, refill with mains water and let the pump circulate for at least 24 hours before re-testing. Rebalance pH, alkalinity, and calcium hardness after the dilution, since fresh fill water will shift those values. Test TDS again to confirm the result.
- 4
Consider Reverse-Osmosis Recycling for Larger Pools
For hotel pools, large villa pools, or any situation where draining is impractical — due to local water restrictions, the cost of refilling, or an occupied property — mobile reverse-osmosis (RO) recycling is the professional alternative. An RO unit connects directly to the pool, filters the water through semi-permeable membranes that reject dissolved solids, and returns purified water to the pool. The process takes 8–24 hours depending on pool size and removes 80–95 percent of TDS without draining. It also conserves water, which matters during Greek summer when water restrictions are common in island municipalities.
- 5
Put a Maintenance Plan in Place to Slow TDS Rise
Once TDS is back in range, slow its return by enforcing a shower-before-swimming rule (reduces body-oil and sunscreen load), using a pool cover to reduce evaporation and the concentration effect, testing TDS monthly rather than only when a problem appears, and choosing lower-TDS chemical alternatives where they exist (for example, liquid chlorine over granular forms that leave salt and calcium residues). In Greece, where pools often run from April through October, a single mid-season partial drain of 15–20 percent is often enough to keep TDS manageable for the full season.
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FAQ
- How often should I test TDS in my Greek pool?
- Test at least once a month during the swim season, and always after a heavy-use period such as a holiday gathering or a week of fully occupied rental bookings. In areas with hard tap water — common across much of mainland Greece and the islands — TDS can climb by 100–200 ppm per month under normal use, so catching it early means a small partial drain rather than a large one.
- Can I lower TDS without draining any water?
- No reliable method exists. Reverse-osmosis recycling is the closest alternative because it returns purified water to the pool rather than removing it, but it still involves running all the pool water through membranes that physically reject dissolved solids. Products marketed as TDS reducers or clarifiers improve water appearance temporarily but leave the dissolved solids count unchanged.
- Is high TDS dangerous for swimmers?
- High TDS is not acutely toxic, but it creates conditions that are uncomfortable and ultimately corrosive. Swimmers often report stinging eyes and irritated skin — symptoms frequently blamed on chlorine, but actually caused by imbalanced water chemistry worsened by high TDS. Over time, elevated TDS accelerates corrosion of metal fittings, pool surfaces, and pump components, leading to maintenance costs that far exceed the price of an earlier partial drain.