Fresh Water Cycle

Question
Greetings, I have past long experience with both Fresh and Marine tanks and was able to keep some koi alive for 12 years in a 90G and a Queen Angel in my 55G.

Have not had a tank for 3 years and am rusty. Setup a comunity 40G high (5 weeks) with Emperor 400 dual wheel and used mini ceramic bio rings in two baskets. Second filter is HOT magnum with polishing filter for initial cycle. Added Cycle at week 4.

Initially added 6 White Clouds and three Swords. One has disappeared (14 days now).
My Amonia is 0 My nitrite is 30+ and my nitrate is unmeasurable since the Kordon Aquatru pillow test kit uses both LR nitrate then a nitrite pillow (plastic pill filled with powder) to test. The nitrite is so high nitrate is indistinguishable.

Have attemted to find dead fish but no good and I do not want to distrub the tank any more.

If I let this rot away at 80F how long and what effect do you think it will have?

The fish are ok so far. PH is 6.8


Answer
It sounds like you have a little bit of. "New Tank Syndrome" Losing that one fish might not do too much to your water. Sometimes the other fish eat the bodies and you may never find that fish. The best thing you can do for the nitrate level is water changes. Maybe 20 percent every week. It takes some time but things should fall into place.