Stuff in the pool.

[chem geek]

I wouldn't add any CYA until you clear this up (and remember the caveats I gave about adding a small amount of CYA in your indoor pool; it's speculative; not normally done, but probably has benefits, but also has potential downsides). The CYA certainly won't help with the tissue stuff you are seeing. Look at this link (and this thread from the same person) about white tissue mold since that sounds like it might be what you have (also more at this link). If so, then it sounds like a very thorough cleaning of all pool surfaces in contact with the water is required and that you could use skimmer socks to collect some of this mold and then replace your filter cartridges/sand/DE unless backwashing thoroughly cleans the sand/DE. Be sure and check your skimmer as well (some sites recommend leaving the skimmer top open so sunlight can get in, but that is not a realistic option for an indoor pool). It also sounds like serious shocking with chlorine is needed, but having no CYA in the pool would normally not require that much chlorine (10 ppm or so) so this stuff must be incredibly resistent to chlorine. It also sounds like sunlight helps kill or prevent this mold from growing, but that's not doable for your indoor pool. I doubt very much that it's calcium since your CH is low (which is fine for a vinyl pool).

Several sites report that the mold grows in the lines so slowly adding chlorine to the skimmer (with the pump running) might help clear the lines by having a shock level of chlorine in those lines. That's not something you'd want to do all the time since chlorine is an oxidizer and continuous exposure at high levels would accelerate corrosion, but for short-term use to get rid of white water mold, this seems reasonable. Shocking to get the overall pool FC to at least 10 ppm and then slowly adding some chlorine to the skimmer with the pump running will hopefully kill this stuff in the pipes and filter.

Some sites talk about bromine being more effective than chlorine for getting rid of this mold, but that's not an easy option for you (i.e. adding sodium bromide) since adding bromine converts your pool to a bromine pool and the way to get it back to a chlorine pool is to get rid of the bromine through chlorine shocking and that may also require sunlight to help that process (I'm not sure, but if it does, that's not an option for your indoor pool). The other product I've seen is at this link which contains sodium carbonate peroxyhydrate which is a strong oxidizer (and alkaline so you need to add acid when adding this product). It's essentially a combination of sodium carbonate (typical pH Up) and hydrogen peroxide (an oxidizer) and is also known as sodium percarbonate. It is a stronger oxidizer than chlorine so it will consume chlorine in the pool (so if you use it, have the chlorine level lower when adding it, then add back chlorine when it's done it's job -- not sure how long that would take), though it is not allowed for use as a sole disinfectant because it is so unstable (so does not maintain a residual). I cannot vouch for any of these products. Perhaps someone else on this forum has experience with this problem and can tell you how they got rid of it.

If this becomes a persistent or recurring problem, then it's possible that using Borates (from Borax) might help prevent this, but unfortunately it looks like scientific studies have only been done to see borate effectiveness against bacteria, protozoa, and algae with the greatest effectiveness against certain types of algae (mold is often susceptible to the same things that kill algae, but not always). Sorry I can't be of more help.

Richard